Air Liquide customer relations

Has anybody had cause to contact Air Liquide customer relations, in Birmingham, UK? They have been ignoring my request to test an empty cylinder I returned to them, via my supplier, who also had problems. I lost £50s worth of oxygen in a week and I am sure I had turned off the regulator properly. Since then I have heard of a smith who had also had gas loss, so checks with soapy water whenever he gats a refill. I only had an automated response to emails until I wrote a formal letter, then I was assured that they “would look into it.” Eventually I wrote to their CEO, in Paris, but still have heard nothing.

Argon, oxygen, C02, acetylene; I'd be hopping mad to find my cylinder short of expected volume too!
Now methane loss........well, that comes with age.
Or so I'm told.