Exhibit 99.23

EXECUTION VERSION

AMENDMENT TO THE CONFIRMATION

Dear Sir or Madam,

The purpose of this letter agreement (this “Amendment”) is to amend the letter agreement dated as of December 1, 2014, as amended from time to time to the date hereof, between Citibank N.A., London Branch (“Dealer”) and Waha AC Coöperatief U.A. (“Counterparty”) (the “Confirmation”) confirming the terms and conditions of the Funded Collar Transaction (the “Transaction”). Any capitalized term used but not defined herein shall have the meaning assigned thereto in the Confirmation. References to the “Security Deed” shall be to the Security Deed as confirmed and supplemented by the supplemental security deed dated on or around the date hereof (the “Supplemental Security Deed”). The Supplemental Security Deed shall constitute a “Document” for the purposes of the Confirmation.

1. Amendments. The Confirmation is hereby amended as of the Amendment Effective Date (as defined below) by:

2. Amendment Payment. Counterparty shall pay to Dealer an amount equal to USD 12,278,276 on or prior to August 26, 2016.

3. Collateral.

4. Representations, Warranties and Covenants.

5. Conditions to Effectiveness. This Amendment shall be effective on the date (the “Amendment Effective Date”) the following conditions have been satisfied or waived:

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If the Amendment Effective Date shall not have occurred by August 26, 2016 (or such later date as agreed upon by the parties hereto), this Amendment shall automatically terminate and cease to be of further effect and the parties shall have no obligations in connection with this Amendment, other than (x) in respect of breaches of representations or covenants on or prior to such date and (y) pursuant to Section 6 below. Each of Dealer and Counterparty agree to use commercially reasonable efforts to cause the Amendment Effective Date to occur on or prior to August 26, 2016.

6. Hedging Costs. If (i) the Amendment Effective Date does not occur by August 26, 2016 (or such later date as agreed upon by the parties hereto), (ii) Dealer has not breached the Confirmation, as amended by this Amendment and (iii) this Amendment is terminated as set forth in Section 5 above, Counterparty shall, upon the written request of Dealer, promptly reimburse Dealer for any costs (including, but not limited to, hedging mismatches and market losses) and expenses incurred by Dealer in connection with its hedging activities or otherwise in connection with this Amendment on and after the date hereof.

7. Continuing Effect. This Amendment amends solely the terms and provisions of the Transaction and the Confirmation set forth herein and nothing in this Amendment is intended or shall be construed as amending or waiving any other terms or provisions of the Transaction, the Confirmation or any other rights of Dealer or Counterparty under the Transaction or the Confirmation. Dealer and Counterparty acknowledge that each of the Transaction and the Confirmation (each as amended by this Amendment) are in full force and effect and are hereby confirmed and ratified in all respects. References in the Confirmation to the “Confirmation” or the “Transaction”, as applicable, shall refer to the Confirmation or the Transaction, as applicable, as amended by this Amendment. Counterparty hereby confirms and agrees that none of the rights and remedies of Dealer under the Confirmation shall be prejudiced, avoided or otherwise adversely affected by this Amendment and Dealer may rely and continue to rely on the Confirmation as if references therein to the “Confirmation” are to such instrument as amended, varied, extended and supplemented by this Amendment.

8. Severability; Illegality. Notwithstanding anything to the contrary in the Agreement, if compliance by either party with any provision of this Amendment would be unenforceable or illegal, (i) the parties shall negotiate in good faith to resolve such unenforceability or illegality in a manner that preserves the economic benefits of the transactions contemplated hereby and (ii) the other provisions of this Amendment shall not be invalidated, but shall remain in full force and effect.

9. Governing Law; Submission to Jurisdiction. This Amendment and all matters and all non-contractual obligations arising out of or in connection with this Amendment shall be governed by, and construed and enforced in accordance with, English Law. This Amendment is also subject to, and incorporates, the jurisdiction provisions contained in Section 13(b) of the Agreement as though, for such purpose, references in such Section 13(b) (as amended pursuant to the following proviso) to the “Agreement” were deemed to refer to this Amendment; provided that in the first line of Section 13(b) the following shall be inserted after the word “Agreement”: “including, without limitation, disputes relating to any non-contractual obligations arising out of or in connection with this Amendment”.

10. Contracts (Rights of Third Parties) Act 1999. A person who is not a party to this Amendment has no right under the Contracts (Rights of Third Parties) Act 1999 to enforce any term of this Amendment but this does not affect any right or remedy of a third party which exists or is available apart from that Act.

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11. Market Abuse Regulation Representations.

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This Amendment may be executed in several counterparts, each of which shall be deemed an original but all of which together shall constitute one and the same instrument.

[Signature page of Amendment]

Counterparty hereby agrees to, accepts and confirms the terms of the foregoing as of the date set forth above.

[Signature page of Amendment]

ANNEX A

For each Component, the Number of Options and the Scheduled Valuation Date is set forth below:

Annex A – 1

Annex A – 2