MTN Contract to Pre-paid

Eventually got my number to move to Pre-paid, now i can’t receive calls, people are telling me that it goes straight to voice mail and others are getting “ the number you have called is in correct please check the number and dial again”

Called customer service several times still nothing, none of they are able to help, they keep on saying dail #35*0000# and this doesn't help either, the worst part is that i still have to other contracts with you guys. Is this how you treat your customers if they refuse to upgrade and migrate to Pre-paid?