This happened to me. I rang each of these agencies once to explain that the person/s they were chasing were not me, etc.. (Make a note of the date & time and get a name of who you speak to.)
This did not stop the letters, so I wrote one back to each of them, stating:
" I have already contacted your company by telephone regarding the matter of (the debtors name) on (date) and spoke to (the representative) and I politley explained that I am not the person of interest to you. However, you persist in sending threatening letters to me. I now inform you that each letter I receive from your company after (give a date of, say, 7 days from the date you are writting) will incur a �50 administration charge to cover my time and trouble in dealing with the matter. I shall send you an invoice on the last working day of each month which I expect to be settled 7 days from that date. Failure to pay will attract a penalty levied at the Bank of England base rate plus 2% until such time as your debt to me is discharged."
Now, don't go getting excited about all the money you'll be receiving.............they usually stop sending the letters, instead :o(