I have an outstanding amount of R513 as per Telkom and they are unable to tell me why

I have an outstanding amount of R513 as per Telkom and they are unable to tell me why . I have requested the phone call that was made when I cancelled and the agent wasn’t able to help at all . I have explained that my contract ended and I cancelled the LTE contract as well . I received Referance numbers for both and confirmed over the call no more payments will be required . But then I was debited and reversed the payment due to poor service and communication. Please help urgently this is affecting my credit score I’ve worked so hard to maintain .