lines keep being blocked

Sincemy upgrades in august 2015 my lines are blocked every month. Every month I have to phone mtn to unblock them. The debit order goes through and they take the payment but then again every month they block the lines. I have asked and asked and asked again to get this rectified but with NO SUCCES. I am so tired of this. I will never encourage someone to change to mtn, their service is the worst.