Sometimes but not all the time a Samsung phone can be region locked.
This is to stop grey imports.
The route to remove a region lock is to use a local sim card in the phone in the region it was purchased and make a phone call for approximately 5 minutes.
If a person has returned hone and the region lock is in place then contact Samsung Support and they may be able to help remotely.
" but the Indian one doesn't work with us sims because it's imei is somehow locked "
An imei lock is a different as this is typically applied to anphobe that's been reported lost or stolen or Samsung have locked it due to the original owner not following a process i.e sending a trade in phone back On time etc.
You cannot remove an imei lock unfortunately as only the original owner can or Samsung can if the original owner then sends back the phone as arranged originally.
Daily Driver > Samsung Galaxy s²² Ultra 256Gb in Phantom Black.
The advice I offer is my own and does not represent Samsung’s position.
I'm here to help. " This is the way. "