If true this is is flipping outrageous!!
If that happened to me I would gladly spend more money doing something about it. There is an accepted phrase to describe this type of activity and it is called "stiffing" (believe it or not). If this is true, it is a typical stiffing situation where the wrong doer relies on the victims shrugging their shoulders and doing nothing more than vowing not to make the same mistake again; it usually means more expense and aggravation to get some satisfaction.
Just thinking about this some more. Shouldn\'t the first port of call be to the CAA? After all we pay them to regulate our training and if people are being exploited I assume the CAA has the power to threaten or ultimately to remove certificates and stuff??