Wow OP. These people are absolute cockwombles.
And they’re deluded if they think they’re going to get £75k more for that house.
I think just agreeing to write a factual statement to assist the EA is fine. You’re only just listing simple facts about a house you tried to purchase. Nothing false or embellished is it? Just a timeline of house buying events.
Now me? I’m petty as fuck. And if there was some need for me to attend any kind of court hearing, I’d be playing the victim card so well, I’d get an Oscar
I also have petty as fuck friends who would gladly make a few inflated fake offers on their house and then magically go AWOL 

Sounds like you’re a lot more sensible than me though! 
I really hope that a wonderful house comes up for you and that this will all be a distant memory and you can sit smugly in your new home, comfortable in the knowledge you dodged a massive bullet 
