Sharks in the water?

I have received a threat of court action for 'late payment' of a debt which allegedly originated four years ago. I did not request any services from the company concerned, don't believe that I have incurred any debt, and have had no communication with them in four years.
A company called 'xxx' claim to be pursuing a debt which their client (yyy) had invoiced by e-mail, and had sent 'numerous reminders' (also by e-mail). The e-mail address they apparently used is not one
which I have supplied, or have ever used, so it's a mystery where they got that from.
In the last four years they don't appear to have made any other attempt to contact me about this alleged debt, apart from the alleged e-mails (despite clearly having my postal address).
Is this the shoddiest of 'shark tactics' you've ever heard of?
Would any court in the land take such a threat seriously?

Hi I have had the same thing where a company carried out work for me, in 2004, I kept asking for an invoice, but they never did and now since the success of my product on the market they are now trying to charge me for 'consultancy work as well as the work requested taking the costs from £450 which I am still happy to pay but now they want £3000 as they said it was their manufacture of my prodcut (I own the patents and gave them the original prototype to copy) that made me successful and that if I don't pay in 7 days they will take me to court, they have sent me about 20 letters like this!
So in answer to your question (I have been to my lawyer and to the courts) they don't have a leg to stand on. I am now pursuing them for harassment and extausion.You may want to send them a similar letter. Dont be bullied by these thugs.