People who take advantage deserve to be taught a lesson.
Is the charter business RYA or local Tourist board Registered?
As at the very least I'd start to copy them on any correspondance just to cause a little extra grief for the person.
How much money are we talking?
If it's enough to be worth their while I know some people in Portsmouth who will purchase the debt from you at @50 to 75p in the pound.
They are very good at retrieving bad debts
A few years ago after a month of trying to get a refund from a company, I spent 20p registering:-
the company name)stolemymoney.co.uk
I made sure it appeared on the first page of a google search for the company name, set out my issue on the page objectively, and sent the manager a link. They threatened me with legal action, but my money was soon refunded on the promise I shut the site down.