MTN not accountable

I have 3 cellphone contracts with MTN, every month the bill fluctuates and there's additional costs that I need to pay. MTN consultants cannot tell me where the additional costs come from, then around the 26th of each month they suspend my network services and this negatively impacts my business. This month I paid a R1000 above the outstanding amount on, MTN still suspended my services and consultants couldnt explain why I cant make nor receive calls. Its ridiculous because I am losing money.