Walmsley31

I have a RX450h 2012 and my rear seatbelt started to fray then when my son went to put it on it ripped almost the whole way through. Now my other rear seatbelt is starting to fray. Lexus say it’s wear and tear and I have to pay to replace them. I thought seatbelt had some kind of warranty. Anyone know of this has happened to anyone else or if they are covered on a warranty.