Contract cancelled but still being harrassed

I have been with MTN since 1997. I have a contract for a stick with a sim card which I took out many years ago. In September last year there was an error on the statement which I queried. Whilst quering this MTN sent me a letter of non payment and stated early settlement termination. So very irritated by this I paid the full amount. Since then I have received letters to say the account is not closed and that I still owe the amount cumulating since then. The contract value is R99.00 per month. Now its going legal - what a waste of time and I will also employ an Attorney to fight this awful Company - I am also cancelling a further two contracts I have with MTN