Hi Gaza,
Well they really are getting desperate aren't they? First threatening a CCJ and then threatening a Stat Demand. Just so you don't panic too much, Capquest are renowned for doing this to scare you into paying, then not following through.
The way this account has been (mis) managed is horrendous. Shambolic.
You really need to get your teeth into it once and for all, to sort it out.
A couple of questions before we sort a letter out:
Did you get a response from the FOS? If not, why not and if so, what was it?
Did you send a Subject Access Request to the original company? I suspect not as it's not been mentioned since.
Thing is, if you want to put this to bed, YOU MUST SAR THEM.
Please, please send a SAR to BOTH the original company AND Marbles. It will cost you £10 each, unfortunately, but you urgently need this information. Do it ASAP. There's a link to the SAR template letter in my blog linked below.
You should also report this bunch to the OFT for using multiple unsubstantiated legal threats as a debt collection tool. Bankruptcy threats for just over a grand on a long term disputed debt with an admission of no CCA. Preposterous! We'll help you with that letter too. I think they fall foul of CPUTR too, in making threats they cannot legally fulfil.
I'll be back when you've answered the questions,
again, don't panic, they're just trying it on, but nonetheless need their @sses kicking once and for all.
Elsa x