MTN Does not care about new customers

Ported to MTN in December19. Had the worst week as I was unable to call out. I can send and receive sms's, recieve calls and use my data BUT I cannot make any calls. This got sorted after about 2 weeks. NOW AGAIN I HAVE THE SAME ISSUE. I'm unable to call out again. I can send and receive sms's, receive calls and use my data BUT I cannot make any calls I've spoken to many consultants. Turned my phone off multiple times, remove my sim. Even tried another cellphone. Please help me.