Cancelled contract

I have been living over seas for the past year and my South African sim card has not been used since last year. Mtn is trying to find an excuse for the reason of why my contract has not been cancelled on their side. I have proof of emails on the 30th of december requesting that my contract be cancelled immediately and then got a response on the 8th of January explain that my account will be cancelled and migrated to pay as you go as I have exceeded my contract date anyway. My last payment should have been January which I paid for. Mtn is just making excuses and taking responsibility for their actions. I am now having to pay for payments being rejected in an account I don't even use as I am living oversea!!! And mtn doesn't even have the decency to compensate for this. I want a letter from mtn stating that my contract has been terminated and transferred to pay as you go. And if one more debit order gets processed I will get a lawer and the police involved.