Vodacom is ****ming us

I have been a customer of Vodacom for well over 20 years and I have never experienced any bad service, until recently. I want to camcell an additional data line I had contracted with Vodacom, which reached contract expiration in November 2023. I phoned Vodacom to notify them of this from May 2023, but they kept telling me to call exactly a month before expiration date. Needless to say I called on December 2023 and they said it would be cancelled after a month, end of January 2024. The cancellation was not done! I then phoned again in March and the consultant confirmed immediate cancellation. And now at month end, Vodacom has debited my account for the cancelled contract. Four months of payments for a contract I have cancelled. What must one do when being ****** by this big businesses??????