........apart from an extremely agressive first approach these guys are no different to Davenprt Lyons and ACS. (They are only interested in getting your cash!)
As such their claim should be treated exactly the same. As the account holder (I presume) you are held totally responsible. (in their eyes)
In reality you have to have either been personally responsible or authorised the action. (in which case seek legal advice)
If the above is not the case then reply and deny. Remember to keep your response simple - any additional information you supply will/may be used against you.
I can also reccomend you visit the chatroom at "beingthreatened"
By the way welcome to the game