To rub salt in the wound a bit further, we later found a charge for the
formal lunch on our mess bills
I'm surprized that there was not the bill for a practise lunch as well!
Charging for services that you had not received was nothing new for the Mess in the good old days - I remember being billed for a guest night that I had not attended. Apparantly, the list came round when I was deployed, and my name entered on the list by the squadron in case I wanted to go. Unfortunately, the squadron forgot to tell me and I went on leave instead. Next month, the charge of about £40 for the function appeared on my mess bill - this was rather high to pay for some damage that had been caused at the function. I rang the mess and told them that I was not there and could they remove the charge - they refused. Several formal letters followed with a few threats etc and a "final offer" not to charge me for the damage! I finally told them that I would see them in the small claims court with their proof that I had ordered the service that they were charging me for - otherwise they were committing fraud.
They backed down.