UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE 14A

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the Securities Exchange Act of 1934 (Amendment No.         )

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CSG SYSTEMS INTERNATIONAL, INC.

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Your Vote Counts! CSG SYSTEMS INTERNATIONAL, INC. 2021 Annual Meeting Vote by May 19, 2021 11:59 PM ET CSG SYSTEMS INTERNATIONAL, INC. 6175 S. WILLOW DRIVE GREENWOOD VILLAGE, CO 80111 D40892-P50923 You invested in CSG SYSTEMS INTERNATIONAL, INC. and it’s time to vote! You have the right to vote on proposals being presented at the Annual Meeting. This is an important notice regarding the availability of proxy material for the stockholder meeting to be held on May 20, 2021. Get informed before you vote View the Notice and Proxy Statement and Form 10-K online OR you can receive a free paper or email copy of the material(s) by requesting prior to May 6, 2021. If you would like to request a copy of the material(s) for this and/or future stockholder meetings, you may (1) visit www.ProxyVote.com, (2) call 1-800-579-1639 or (3) send an email to sendmaterial@proxyvote.com. If sending an email, please include your control number (indicated below) in the subject line. Unless requested, you will not otherwise receive a paper or email copy. For complete information and to vote, visit www.ProxyVote.com Control # Vote Virtually at the Meeting* May 20, 2021 9:00 AM MDT Smartphone users Point your camera here and vote without entering a control number Virtually at: www.virtualshareholdermeeting.com/CSGS2021 *Many stockholder meetings have attendance requirements including, but not limited to, the possession of an attendance ticket issued by the entity holding the meeting. Please check the meeting materials for any special requirements for meeting attendance. V1

Vote at www.ProxyVote.com THIS IS NOT A VOTABLE BALLOT This is an overview of the proposals being presented at the upcoming stockholder meeting. Please follow the instructions on the reverse side to vote these important matters. Board Recommends Voting Items 1. Election of Directors Nominees: 1a. Brian A. Shepherd For 1b. Frank V. Sica For 1c. Silvio Tavares For 1d. Tse Li “Lily” Yang For 2. To approve, on an advisory basis, the compensation of our named executive officers. For 3. To ratify the appointment of KPMG LLP as our independent registered public accounting firm for fiscal 2021. For NOTE: Any other business that properly comes before the meeting or any adjournment or postponement of the meeting. Prefer to receive an email instead? While voting on www.ProxyVote.com, be sure to click “Sign up for E-delivery”. D40893-P50923