Stuck on unlocking please wait

Hello!

So I have an iPhone 5 that's stuck when trying to unlock the SIM card.

Last year, before I put it aside, it was fully working! There's already this question on this forum, but my story has a twist: I cannot access Settings because the phone isn't activated (did a factory restore before storing it) and my computer asks for a valid SIM when I try to connect it.

The phone is also carrier locked, but I've tried unlocking it with two SIM cards from the same carrier. Do you have any suggestions?

Thanks!