A third party using my account to activate its decoders

I had some time in 2022 closed my DSTV account number:89.....33 because I had started using DSTV NOW APP and opened a streaming account number:14......95. On about 13 June 2023 I received an sms from Multichoice debt collectors demanding that I pay an amount of R180 under the DSTV account 89.....33 I was shocked, as I had closed the account and settled it everything thereto. I phone the customer care number and I was told that in deed I owe the amount as the explanation was not satisfying, I had to pay it. On 27 October 2023,I received a call from Multichoice offering me a Debit order special wherein you authorise a debit order and you get discount. I was interested as I was giving out my details to the MultiChoice employee, i realised that she was not talking about my streaming account but talking about the account that I had closed in 2022. She proceeded to inform me that I have 2 two decoders active under my name and account (that one I closed in 2022). I was very upset to hear that I called multichoice to no avail and used their WhatsApp line to complain but no help was or proper explanation why my details were used to activate Decoders belonging to a THIRD PARTY