Help please

Booked Heathrow to JFK for Nov 11-15th back in August. Picked our seats as soon as possible back then. Logged in today and can see the have changed planes to neo which has 16 less upper class seats that the 1000 it was previously listed as. Also my seats are blanl and can’t selected new ones as all already selected. I had seen previously the 1000 was all booked so looking like I am one of the 16 people who wouldn’t get upper class seat. Virgin just keep
Saying I am booked as upper class and won’t assist. Any ideas or help

Are they selling tickets for that flight in UC still?
Sometimes they do block off seats for manual check in.

If it’s showing UC as sold out, I’d get in touch with them again to see if there is anything they can do.

If it is sold out, I would try asking them to put you on a different flight