Mtn not helping out

Its been more than a year im trying to change my contract. Ive moved from South Africa and since then ive been emailing MTN to either cancel my contract or downgrade it to MTNchoice zero. They are deducting money from my account and my sim is in no use. I email them all the time and when they come to a conclusion to help me out. They don't reply to my email. And then again money gets deducted from my account. Such a horrible service they are providing