Theft on a corporate level

One of my cellphone contracts was cancelled, letter for cancellation sent on 09/07/2025, according to my knowledge contract was ending end of that month. According to Vodacom I upgraded the contract in July. The contract was eventually cancelled in December 2025. Debit orders were take for 6 months after I sent a letter for cancellation. According to the person I eventually got hold of two weeks ago there is no credit due back to me as they are sticking to the fact that I upgraded the contract in July. I have requested the voice recording on numerous occasions to ascertain whether this is correct as I cannot understand how I can upgrade a contract I had already cancelled. They have not been forthcoming with the voice recording leading me to believe that their version is not correct. I have 8 other contracts with this company and as they become due for upgrade I will cancel as they are quick to take money that is not due to them and give absolutely no explanation when they are asked why.