Poor service from the call center

Poor service from mtn call center.. I finished paying my contract in January, I went to the shop to ask them to change it to prepaid, the consultant said they only cancel at the branch but changing to prepaid i have to call the call center. I've been calling since the 5th of February Holding for an hour but when they finally pick up the phone they hang up after I explain that I want to change from contract to prepaid. Now I'm not even sure if they changed it or not.