No one willing to assist

My iphone 5 switched to prepaid from TopUp a few days ago without any warning. <br> <br> Thereafter, my internet suddenly stopped working, followed by text messages - even though I had data and airtime. <br> <br> My phone is completely useless to me now. We don't have internet at home and without wifi the phone just doesn't serve a purpose.<br> <br> I've tried calling the call centre, and received no help. I tried going into the MTN store in Garden Centre and was told by the assistant there that she didn't know what the problem was, and that i should call the call centre... It's like groundhog day of bad customer service!<br> <br> I am now stuck with a completely useless phone - unable to business and unable to feel secure when commuting or home alone.<br> <br> Please can someone in management from MTN call me ASAP because this problem is getting absolutely ridiculous!