Try calling Heathrow Lost Property office - this is handled by a third party company called Excess Baggage Company... if you haven't done so already.
Contacting the lost property office
Telephone number: 0844 824 3115 (UK only).
If you are calling from outside the UK, please call +44 (0)20 8634 4130
Phone lines are open every day 09:00 – 17:00 UK Time.
Email: lhr.lostproperty (at) bagport (dot) co (dot) uk