CONTRACT CANCELLATION

Worst service in contract cancelation. My 24 month contract is about to expire on the 29th of December 2021 that I took out in November 2019 and today, 07 December 2021, I phoned to cancel my contract and to my surprise they told me that my contract only expires on the 28 May 2022. No where did I changed the period of the contract or agreed to a 30 month contract so where did they get the consent from? This afternoon a sales agent from Vodacom phoned me for a contract upgrade and I declined and expressed my dissatisfaction towards her and she told me that according to her system it reflects that my contract is about to end on the 29th of December 2019. So how the hell is it possible that Vodacom's system reflects different contract end dates? And who gave them permission to extend a 24 month contract to a 30 month contract without consulting with me and with no defaults on my account?