over billing my account

they have over changed my bill by 361 when I ask what is it for no one has an explanations and I am being told to pay what it on my bill, I cant pay for something I didn't sign up for or use at all. this has been happening for a year now they cant explain things they have added on my contract. their shop in Iren Village Mall they do wrong things and don't help clients they ported my MTN to contract while I clearly ask them to port to prepaid, every time I go the shop they do more wrong things are right.