Cant transfer from contract to prepaid in peace

I had a two contracts with MTN. one was due for an upgrade. They didn't have a good offer for me to upgrade. Ive been requesting for that number to be transferred to prepaid. They signed me up for another term without my consent. They are deducting double the amount i was paying and they also halved the amount of data. now i'm under dept review as i refuse to be paying for something i didnt sign up for.