Jet Airways — Web check in

Address:	422401
Website:	www.jetairways.com

I recently tried to web check in but my seats were pre allocated and when I tried changing my seats were pre occupied.
I web checked in at 24 hrs exact before departure and wasn't able to get my seat according to my Choice I contacted the service centre and they don't have any answers except it's computer generated or it's a coincidence I've three different PNR two were allocated seats and others weren't how is this possible even if I haven't checked in