I'd not bother much with an e-mail, but do check the contacts in
this thread, or try the local number from Serviberia, found
here.
That reveals 0 870 609 0500 (spanish & english) 00:00 - 24:00 Lt. Monday to Sunday for the U.K.
As to your avalanche bag, Iberia says:
Avalanche rescue backpack, one (1) per passenger, equipped with a flare device containing less than 200 milligrams net of Division 1.4 S explosives and less than 250 milligrams of Division 2.2 compressed gas. The backpack should be packaged so that it cannot be activated by accident. The airbags in the backpack should have pressure release valves.
Allowed as checked luggage YES
Allowed as carry-on luggage YES
Allowed on passenger (on person) NO
<
link> (probably you have seen this already)
If yours contains no explosive charge and meets the standards otherwise, it should be fine - I would print out Iberia's page, and perhaps put the bag into a duffel or other bag to "disguise" it and minimise hassles - including theft.
Frankly, I do not think it will be easy to find someone knowledgeable in general customer service communications or offices. Good luck, and may the volcanoes sleep...