Unacceptable billing

I have had my account with MTN for theongest of time where I have for the most part never ghad any issues. However since last year December My bill has been 4 times the normal amount. I have queried this with the accounts department on various occasions yet no responce from them to date. I made it very clear that this account will not be paid until I have asolid answer as to why all of a sudden my bill has tripled. Still no responce. I am at a breaking point where I will now rather move to a different service provider.