In this case, the suggestion was not to call BA, but to call AA. Try http://www.saynoto0870.com to get a free phone number and/or reduce call charges. Calls to free numbers are also free using Skype, wherever they are in the world (so if you have a toll-free number in the UK or US for example, you can call that for free from Spain if you use Skype).

They may be able to reissue the ticket from their own stock and slot the earlier flight into your itinerary, either now or after you have flown the outbound flight.

Good luck.