I am very unhappy with the way mtn is *****ing my credit scores up

I am very unhappy with mtn ,in the last few months mtn has been taking money and putting money back into my bank account,and they are charging me for there been no money in my bank account when they is money and the bank has been charging my money for every time my debt gets returns I have when to the store 7 times and they keep saying that they off line .this is very bad for such a big company .????