The sim holder is probably damaged. There is a contact in there that opens when a sim is inserted. If the contact doesn’t open it will not detect the sim.
You can check this as there is a hole in the top of the holder above the contact but you will need to be careful when removing the silver heat sink that none goes into the holder, this heat sink serves no purpose and does not need to be replaced. You will only need to remove the screen to check this contact.
Sim out
[image|2649022]
Sim in
[image|2649025]