Changed Sim but wrong iPhone Number on “My number”

I recently changed to a new sim and took my old number with it since I’ve finally memorised it. My iPhone (it’s 15 proMax) kept giving me notifications once the sim was activated something along the lines of in ‘X number of days my number will no longer be of use’ or something like that. But I didn’t do anything because I was under the impression that once my sim was fully activated my old number would just automatically be used rather whatever was the initial number of this sim as was stated on my new sim account. BUT then once the X number of days happened I could no longer use iMessage or FaceTime and when I tried to check what was going on. In settings on the mobile service my old number that was supposed to be brought over by my new sim suddenly had ‘No Sim’ next to it even thought it was set as primary and the number of that new sim was instead used as primary and had ‘On’ next to it. So I wanted to see if I could fix it and tapped on my old number and instead it somehow got deleted! I then called others and got them to delete my contact to test what my number was and my old number is still the one that showed on their contacts. But on ‘My Number’ on my iphone and the Mobile Service both shows the number that came along with the sim. I now don’t have access to iMessages or FaceTime. Please help! I’m at wits end trying to fix this.