Inability to receive calls from other mobile numbers

I ported to Telkom mobile a couple of months back and since the day I ported I haven’t been able to receive calls from certain people who call. There are people who can call me and there are people who can’t. It isn’t a network specific issue as I receive calls from all networks but not everyone. I called the call centre three times, they make me restart, use dial up strings etc but nothing works. It is incredibly frustrating having to deal with this. I am tired of calling I never thought being with telkom would bring me so much issues.