As a freelance instructor, this happened to me on more than one occasion and was always because the company was in financial difficulty. You think by helping out and waiting, that things will improve, but believe me, it's time to move on. It's usually the start of a downward spiral. Some managers can't manage for crap, and treat their staff with contempt.
I'd refuse to work any further until i'd been paid for the work already done. Also, if you signed a contract which states the day you will be paid etc, they have breached your terms and conditions of employment. I'm betting you didnt sign any sort of contract???
The helicopter industry has to be filled with more chancers than could be believed. Don't for one minute feel any loyalty towards an employer these days. You're just a bum on a seat to them.
Sterling Helicopters at Norwich by any chance????