Telkom blacklisted me for 8 months after 2-year contract ended

I took a 2-year Telkom contract in November 2023. The contract was supposed to end at the end of October 2025. I paid every month by debit order without fail until December 2024 when I changed banks for personal reasons. Despite the contract ending, Telkom kept trying to debit my OLD bank account. Because those debits failed, they now show me as 8 months in arrears on my credit profile and have handed me over to debt collectors - I think to Daya attorneys if my memory serves me well. My credit score has dropped badly and I am blacklisted for an account that was paid correctly for the full contract term. In fact Telkom owes me a refund because they debited me for November and December after the contract end date.I call Telkom and agents drop my calls because they can not provide the solution. Debt collectors say they will report back but nothing happens.