A day light *******!

MTN is the provider that will deduct more money than the one agreed on contract without the customers consent, I have queried the same issue and was still not resolved, I have been charged more than R700 for the last two months and I was told that it's because I have exceeded my credit limit, they have charged me for using data on my other phone where as I have subscribed for 20 gigs and I don't finish that data, the real question is why am I charged for exceeding my data usage whereas I don't even finish the data, I have two contracts one for 20gigs of data and one for my phone, I pay 199 for the data and 269 for the phone, so as up u can see apparently MTN has made ways to make more money with my bank account and deduct R718 on my account, for what? MTN is pushing serious ***** on my bank account.