Cancellation of MTN contract

I am trying to cancel an expired contract and MTN now wants to bill me a full subscription. When phoned on the first to do the cancelation I was told to phone on my billing date now I get another excuse and the lady who assisted me said I either take another contract so I don't pay the full amount. Why am I forced to take another contract? Can I not just cancel my subscription, pay pro-rata and proceed with my life without being forced to stick with MTN. This lady keeps telling me to take 100GB or 200GB???? What the hell? All I want is a cancelation. Stop forcing customers to chose a service when they want a service to be canceled