The airline
Credit Card/Debit card
Continue to 'bombard' the British Embassy (for the attention of the Ambassador) demanding your treasured and important documents be returned,
You must already know by now just how slow the wheels of Government Agencies grind.
Keep the pressure on. E-mail Theresa May, David Cameron, your MP etc
Keep being a pain until something moves. Involve the media, your local newpaper etc.