Has anyone had any success getting lost property at Bilbao airport and, in absence of me flying back to Spain, how?

I left my expensive sunglasses on the flight to Heathrow from Bilbao. Annoyingly, they went back on a return flight, and are now in Bilbao airport and I'm in the UK. While the lady on the other end is very nice and I have been in contact with them, ultimately, the airport is refusing to post them back (I said I'd pay) or offering any suggestion on how to collect them.

I have looked into various courier services and googled the options but they seem to be lacking. Previous post got deleted and I wonder if it's because I named the courier service but to explain problems which I encounter

(1) - need to box them up. I won't be able to do that. I'm in the UK; or

(2) - seem to only accept Spanish home address; or

(3) - seems to only work (largely) in Greece; or

(4) - will not accept my enquiry (says fields are incomplete, they are not), email bounced back and won't respond to whatsapp.

I've even looked if there's a cheap flight to do a weekend trip, there isn't.

Any suggestions welcome.

Thanks