Poor service

I have data contract with MTN and I requested to cancel the contract since I was no longer happy with their contract. I called their call centre and they advised me to go pay at the store and call them. I paid using my card and they told the payment does not appear on their system for like a month. I sent an email to their complaint department and they asked for proof and I sent them. They told me they will deduct more money from my account and I allowed them since I don't want anything to do with them. I even destroyed the sim cards but they keep on deducting that amount that they were deducting before and now they don't reply to my emails. Ngidinekile angifuni ukungasho mxm