SIM card

I sent an iPhone SE back to carrier for upgrade. They wouldn’t accept it because the face was scratched which it was but I will go to my grave insisting it wasn’t scratched when I put it in the mail. Now the SE doesn’t have phone capabilities. The new phone I received when I thought they would accept the old one works great. They are telling me to switch out the SIM card which doesn’t seem right to me. Is it possible that they put the my original SIM card in the wrong phone? I hope this makes sense!