refuse sim and unfriendly

I have been struggling with my new contract since I walked into that terrible store. Firstly, they recommeded an absolute ******* phone on an expensive payment. The m4aqua. It has no internal memory and is soooooo slow. I was looking at an iphone and they told me it was *******. Then when I got the phone, I was not aware that it uses a nano sim. Couldn't use the phone till date. I wanted to get a nano sim but they refused to accept my eskom account as proof of residence.they told me its not their problem. They have rules. With a very nasty attitude I might add. I mean, we had all the documents with us when we renewed the contract. Now I have the old sim in my blackberry and I can't use anything on either the bb or sony. The personnel at delmas branch also post grievances about customers on their facebook pages and target customers. How can I cancel this contract? I want to severe all ties to MTN. Delmas also has a problem with calling to landlines. Mtn has already cheated me out of my 16 year old number and now this.