Can't help with the initial question but assuming there were no extraordinary circumstances involved in the flight changes on the outbound remember to claim compensation from BA for the involuntary reroute and arrival at destination more than 12 hours later. Applicable for all passengers on the same booking too. Might go some way to make up for the hassle you've experienced.

Edit to add notice there were two cancellations on the day so potentially claim for original flight cancellation and separately for second flight cancellation and reroute.