Wrong contract and debit order

MTN have loaded my new contract with the wrong debit order amount. Have contact them several times to sort it out, every time the same answer "we have send your complaint to the sales team, still waiting for feedback from them". This is going to be the 4 month that the wrong debit order amount will go of my bank account. If I stop or reverse the payment, that will have adverse effect on my credit profile, but this company just don't care, so what must customers do. The joke us that I have to go thru this scenario every two years. Every time I my contract expires, and I choose a new/different contract plan this happen. This company have one of the worst customer service in the world. But going over to one of the ofter companies isn't a option, there service is also useless.