Contract upgrade

I upgraded my cell contract at the end of Feb 2015 at MTN in the Kolonade mall. With the sim swap as the phone required a new sim I was told it takes 48 hours to activate but a week later it was still not working. My son went to MTN in Rustenburg and after 2 days he could use his new phone! He kept on having problems and at first thought it may be the phone. He went to MTN in Rustenburg and they told him it was the sim card which they swaped and funny enough within about 2 hours it was activated!<br> At the end of April I recieved a sms that I have nearly reached my usage limit. I checked on my account and saw that I still had free airtime and data but my son exceeded his monthly free data and airtime! When I upgraded I told the lady working at MTN Kolonade that he must have a top up contract same as his previous contract which means he cannot exceed his free airtime unless he buys extra data or airtime. I whent to MTN Kolonade on the 21 or 22nd of April and queried this and they told me that there was a mistake made with the upgrade and that they will fix it! Today my account was suspended because I exceeded my monthly limit! I want to cancel the contract but must pay cancellation fee