I bought a fiat ducato van from a dealer and three days later it went wrong

I took it back and he replaced an injector, charged me a further 200 quid and said it was OK now. It made no difference what so ever turns out the engine is down on compression one one cylinder and diesel fuel is entering the sump making it unusable. I have written two letters to the dealer saying I'm not happy and either want it fixed properly, a partial refund for a new engine or a total refund, but am getting nowhere. Do you think I should now take this to court (looked at a blog online looks like he's done this to a few people).