Mtn continues to overbill

Mtn is a real stuff up and I honestly feel tortured by them because they have me trapped in a contract. I have on more than several occasion complained of their overbilling, arranged for a conversion to TopUp so as to not go above my minimum subscription charges, which application I was told was granted, law and behold I have to pay an exhorbitant amount again. I am done, I will not renew this contract and want nothing to do with Mtn anymore, honestly don't feel any pity with your Nigerian issues, to me you are greedy ******.