unsatisfying service from Auto & General

I took a contract with MTN on the 11 September 2013,my contact expired this year,i was called by MTN representative for upgrade. I stated that I will not be interested in an upgrade due to financial problems, to my suprise I got top up on the 14 October from MTN. I called asking them to reverse but all I got was being sent from pillar to post. I later received an email that says my contract is still active. How can it be as I cancelled. MTN wants to rob me by forcefully topping my sim and *****ing my money. My contract with them ended, this is so unfair. Their call centre is full of rude people who don't give out information, they just trap people to be paying them even after the contracts have ended.