Refusing to accept my notice to cancel contract

I'm trying to cancel my contract and they are making it impossible to do so as they claim I'm behind payment yet their records show I pay every month... I'm trying to issue a month's notice so they cancel my contract but they're telling me my account is on Collections and they can't cancel(which that on it's own is a problem for me).... I need assistance immediately as I do not want to continue paying for a contract that's ended because of these technicalities that benefit MTN...

Number in question is *** I am Sinethemba Gabada Email: *** MTN pin 8403