I’d have said you could change or cancel the flight as it’s a flight cancellation. I’ve done it before and got a refund on a journey I wasn’t going to make as the new timings weren’t suitable for onward connections .. I think. One had moved 20 mins or so. That argument is a bit lame if the new departure time is the same. Did you book with BA or AA? If AA I’d say you’ve got a strong chance of rebooking