personally I would buy a crap old banger for £50 with some MOT on it.
Insure it, 3rd party only (your will only need to do it for a month) and just block them in and go away on holiday.
By the time the documents have gone through DVLA and the police can trace the new owner, you will be back from your holidays. Sell you car to the scrap yard, ring and cancel the insurance and its cost you next to nothing. Certainly cheaper than solicitors letters.
They will have learnt not to mess with you.
Lets just say, people know better than to mess with me. There are ALWAYS legal methods to get even.