Just had an email from BA come through telling me that my LATAM reward flight got cancelled and that they've automatically rebooked me on a different flight that day.

I've just called the Gold Line to change to a different flight instead (earlier rather than later) and got told that they can only move me if there's Avios availability. It would be free of charge because it's an unwanted change due to a cancellation, but they said they can't do anything without rewards space.

BA are usually happy to book me onto whichever flight I want if there has been a cancellation of a rewards ticket and I was expecting it to be the same with LATAM - is the agent right or should I just try again?