I swapped my sim on Christmas Day when I moved to an iPhone 12 and a 5G SIM card. Since then my signal is erratic at best. My signal drops out all the time, I can’t make or receive calls. I spoke to O2 customer services and they sent me a new SIM card but it’s still the same. I spoke to Apple who said it’s not the phone. What do I do now? My phone only works on wifi, it’s barely a phone at this point.