Pensioner billed for cancelled account

On the 7th November 2021, i paid my account to a ZERO balance and followed the instructions set out by the staff to the T. i called the call center and confirmed that the account was paid up to a zero balance and that the account was closed. Ref***7A. I had received no communication as expected due to me not having an account anymore. I am 73 years old and i am now being harassed by debt collectors asking m for more than R700 .. for what . i am not responsible for staff that do not know how to do their job. i did not get sent a statement of account nor was advised o any outstanding balance. I WILL NOT PAY .. close my account and if you force this issue then i will go to the credit Ombud and state that TELKOM does this underhanded way in which to further indebt their old age customers with out following the proper processes.