Sorry to hear that.
If you have the e-ticket number (13 numbers in a NNN-NNNNNNNNNN format. BA tickets generally start with 125), then you can retrieve by entering the e-ticket number on the website of Saudi Airlines. Their manage my booking engine displays reservations of most airlines. It also displays the 6 digit Amadeus code, required to access the booking on the British Airways website.
Edit: I tried a ticket issued by British Airways (starting with 125) and the Saudia website returned an error. You're better off trying it on the Qatar Airways website. Click "My trips" on the Qatar airways homepage. If the form doesn't immediately recognises the e-ticket number, the you might have to renter it on the next page, where you're show three options (booking reference + last name, Qatar airways privilege number + last name,
or E-Ticket number + last name).
https://booking.qatarairways.com/nsp...rievePnr.xhtml