Bill overcharged

I’m not happy with the service I’m getting from Webafrica billing department, all of a sudden my bill has changed , I sent emails and they even bother to call me and explain this whole situation, it’s frustrating because I’m not getting answers I need, the agent who was helping me is no use , according to my understanding my bill it’s what I have on the contract now all of a sudden there’s an added amount on top of my bill without my knowledge this is ridiculous and acceptable