Just some more after thoughts - lol
Make sure the people you get 3 quotes from have a current waste carriers licence - ask to see it, reliable companies, disposing off waste, within the law will have no problems letting you see it. If you employ someone without one (obviously cheaper) you will be held liable as well if it's flytipped - current fine upto £20,000 I think.
When you write your letter putting him on notice, send it recorded delivery. You may wish to ask him who court papers should be addressed to, him or his parents, that might make him think, and show him you are serious.
Before you apply to court, you will obviously have to have waste removed to show you have incurred a loss. You can also include any additional cost's you have incurred in your claim - have you?