Hi, I have a problem with a new iphone I added onto my o2 account for my sister who is an existing o2 pay monthly customer like myself. I took the o2 pay monthly sim out of her old mobile (iphone 15) and put it in the new iphone 16 pro max and nothing happened. There were no bars. I tried 2 x other o2 pay monthly sims from friends and their sim cards were fine and there were 3 bars and signal. I thought maybe there was a problem with the sim so went to o2 shop and got a new sim but the issue is still the same. Could my sister's existing o2 number somehow be linked to her old mobile which is stopping it from being used on the new iphone 16 pro max?
