Julie,(posted 7883 days ago)All good advise in the above answers - please don't worry too much about the threats, after all, that's all they are at present, I've been trying to deal with these people as well.
I'm a believer in "giving as good as you get". They are basing their demands on your so-called "refusal to co-operate". Therefore your reply to them should be based on their "refusal to co-operate" with you in providing you with proof, documents and answers to your questions and queries. I have learnt to fight fire with fire with DLA, and they don't like it.
Their reply may appear even more threatening, but when pushed, they can only go so far. If they cool off after an exchange of such letters and start appearing to be a bit more reasonable, do you think they have a case??
Good luck
Stephen