I feel sorry for you -easily done. Could you not sell your ticket-non transferable?
I've changed my times with other airlines paying fees like 20-50 quid.
I booked a first class ticket for £2300 a few years ago but had to change plans within a week.
I had to wait 3 months for BA to sort it out-phew but it was 6yrs ago.
BA also detroyed my luggage on every trip. Personally I think they just like customers as their service is shocking but only because they were in debt. So to get rid of debt they harshened up but the customers get annoyed so they go elsewhere. BA got in debt and in trouble and made dumb choices.
I fly Qantus or Emirates if possible. JAL were great and Malaysia.