Ambassador, British Airways; FlyerTalk Posting Legend
Join Date: Apr 2012
Location: Leeds, UK
Programs: BA GGL/CCR, GfL, HH Diamond
Posts: 42,977
yes you often get the seat change email a little bit before you actually get the cancellation email itself.
the agent should be able to remove the cancelled flight. it may need to be sent off for ticket reissue, and of course manual calculation of a part refund.
the email is a bit misleading though as you have actually been moved from a BA flight to an identically timed IB flight with a BA codeshare. Your BA flight has been cancelled.