Small Claims Court
I had a similar problem (long boring story) but I solved it extremely quickly by advising the company that I would take them to the "Small Claims Court"(SCC). They laughed at me.
I approached the "Citizens Advice Bureau" who gave me a SCC form to complete which, I did. I included my £10.00 fee and within 4 weeks received a cheque from the company for the full amount plus my tenner.
It's a simple procedure, basically you write an essay on your position and why you feel aggrieved, the court actually sit in session and hear your complaint and pass judgement in the absence of either you or the people you are claiming against (I think that's how it works anyway).
Give it a go or at least threaten him with this action, if he laughes, do as I did, get the bas***d.
Buy it & Use it, then sell it and buy something bigger