Hi KB - I can't really offer any advice other than to try and get in touch with GT.
They have a web site :-
https://debt.grant-thornton.co.uk/why_gt.php
and there's an 0800 number on there. I had my letter from Debtmatters as well but there was very little detail in there other than what appeared to be a generic email address, but I think you need to act quickly.
Presumably you have kept all documentation from Debtmatters, in which case there should be some kind of reference number on it so that at least they know your case number.
I guess it really depends how GT have divided the cases - perhaps one IP may have transferred to another or they may have divided it by surname. The only thing I can suggest is to call the 0800 number on the site and see if anyone can help or at least point you in the right direction. It doesn't say what time the lines are open until but it's always worth a call - it is free !
Good luck - sounds like you're in a real pickle.
There's light at the end of the tunnel - it's just that sometimes the tunnel seems so long.
IVA Complete June 2009