the problem in my case and perhaps many is that the sim tray is badly designed it’s too deep between the sim and connectors so it’s not flush on the connection side, that minute gap stops it being read, the sim has a spacer around it so when its partly inserted gently push down so it drops, you’ll hear a click it’s still in the spacer but with a better connection, it worked then stopped so i opened it half way and pushed again, it’s now fully connected, this is an old question but still needed an answer for my old phone i’d given up on….