Should I take any action.
For a start, you should stop blaming Moorcroft Debt Recovery. If eBay has passed them your details for recovery of an unpaid debt it's eBay you have to blame if the information provided is incorrect.
Why do you say that you don't have an account with eBay? You are registered as both a buyer and seller, and have sold at least two items in the last month.
You don't have anything to fear from debt collectors if you don't have a debt! Firstly, are you absolutely sure that this is true? Check your records carefully Sellers are liable for all selling fees incurred on eBay, and for the cost of refunding buyers if they win a case under eBay's money back guarantee.
If you are satisfied that you don't owe eBay anything, contact the debt collectors and say so. It will be up to them to show what eBay claims you owe. It wouldn't be the first time eBay has set debt collectors on to the wrong seller!