Account cancelled and settled

I sent an email to Telkom in Jan 2020 to cancel our phone line. I received a response on the 27 of Jan 2020 that the line has been cancelled.

The last bill I received was dated March. I settled the amount in two parts. The second payment I made early in July 2020.

A year later Telkom started emailing and calling me informing me that my account is outstanding. They've been doing this non-stop until currently. I've sent proof of payment to numerous people. Not sure what they do with the POP. They tell me they'll update their records, but then I get an email or call again.

I'm so frustrated and tired and want this issue to be resolved.