Unable to connect a call

I have one friend who I am not able to call for some reason. Whenever I try a message comes up saying 'the wireless customer you are calling is not available' I cannot text this person either. Calling them on whatsapp doesn't work either.

The strange thing is they have not blocked me as they can call and text me easily and I can answer their calls and speak to them but then I cannot seem to call them by return. I can call them from other phones and numbers just not my number.

I tried calling t mobile about this a little while ago and told them the issue but they never got back to me.

Is anyone able to shed some light on this?