unable to phone certin contacts

I have an issue with my sim card/number. When i dial certin number that are both on and not on my phone the automated message says that i donot have are time. But straight after that i phone a different number then it dails that number. No one at MTN knows what is doing on. Customer care is just usless. I HAVE OVER ENOUGH MONEY ON MY PHONE. At this point I want to port my number out of MTN.