You need to open an unpaid item dispute within 32 days from the sale for any non-payers.
Once the dispute is closed without payment you can get their feedback removed.
You seem to have forgotten to register as a business seller, which you clearly are.
You will then have to operate in accordance with the Distance Selling Regulations as well as telling the taxman.
Ebay and the Inland Revenue are working together to weed out all the unregistered business sellers.