UNAUTHORISED CONTRACT

My contract came to an end in December, I was explicit I dont want to renew or upgrade to any package but be migrated to prepaid. Instead they still put me on monthly package i did not request. How did i find out...by my phone being suspended...they say I need to wait for the telephone recording for my line to be activated or pay the service fee....I DID NOT ASK FOR THIS MTN. YOU ARE FORCING ME INTO A CONTRACT!!!!!