Hard to claim for lost phone.

My son lost his iphone which is covered by apple care plus theft/lost. But he couldn't claim the lost phone because he could't go to icloud.com. He doesn't have any other apple product connected to his icloud. I called the support and followed the step to use my phone number instead of his lost phone number. Apple says they will contact my phone after 13 days. I haven't got any notice from apple after the wait. I tried to go to the icloud site but it still use the lost phone number. I called the customer service and they say I have to go to my phone carrier to get the temporary sim for the lost one. But It'll be of no use cause we have changed his phone number about one week before the lost. What I have to do? How come the lost claim is so difficult and no personal visit to discuss this tough situation in the apple store? Is apple store only for selling their physical product? Why they are not do service their insurance product in the store? I am really frustrated and disappointed at apple's service.