iPhone XR no service

My wife’s iPhone XR is not reading her giffgaf SIM card I have tried basically everything, it has been to the phone shop and had

new sim tray

sim port cleaned

new SIM card

Also the shop today has paid to have a check on the phone and has come back fine so it is not network blocked

or phone blocked and they carnt get to the bottom of it so they have told me to contact apple

many thanks Aaron