MTN - not customer orientated!

I have had a contract with MTN for a few years now. For the past 3 months something has been "eating" my data. It happens at the same time of the month - 3 weeks before I receive my new data. I have closed almost everything on my phone, that uses data, and yet it still happens. It took 257MB in 29 minutes, while I was at work (not even being on my phone). I've been trying to get a URL list from MTN for the past 3 weeks now. To see what link I might have activated that takes all my data. All the agents (in the shops and on the phones) just have these long excuses, but no-one is helping to sort this out. I even logged a complaint online - NO RESPONSE! What can I do to get rid of this contract, if MTN is not bothered to get to the bottom of this issue?? I even got a sms to say that my case has been resolved. Ref nr 1- ********** 6842. Resolved... HOW!!! MTN sent me a sms to say that they will load my new data on the 11th, and not the 14th of each month anymore. They couldn't even do that right!