Cant get Telkom cancelled

I cancelled my service 15 - 26 February 2018 and paid a full month in March 2018. I still get accounts. Calling in they agree that my service has been cancelled and I am in credit, however the accounts keep coming, every month higher and i dont know what it is doing to my credit record.

I call in monthly to query. Latest reference nr was: ********** 4.

What more can i do?