How many times must a pay a permanently terminated account

MTN, how many times must I pay the same account?

Last year I paid R3,500 and received a paid-up letter. Last week, MTN told me I owed R637.12, which I paid in full, and I was again issued a paid-up letter.

Today, I was told I owed another R200 due to a “miscalculation.” I paid it again.

This is completely unacceptable. How can MTN repeatedly issue paid-up confirmation and then come back with another amount?

I want a clear explanation, a full account reconciliation, and written confirmation that my account is now R0.00 with no further charges.