Routing issue: People can't get through

So I have been having this issue where certain people can't get through to me on my Telkom Mobile number.

What happens is that when they call, they get a message saying 'the subscriber is not available on the MTN network'.

Originally I ported my number from Telkom Mobile to MTN so I'm sure it has something to do with porting and routing the calls through.

When I went to a Telkom Mobile store they said all that they could do was a sim swap. My brother had this issue with MTN and a sim swap didn't work; they had to sort out the porting properly.

I would appreciate if someone could assist as I would love to get this resolved speedily.