Try ringing them back and refer them to the following link that outlines eBays policy. 

If the initial customer service rep won't remove it - request to speak to a supervisor.

http://pages.ebay.com.au/help/policies/defect-removal.html

Can a defect be removed? We automatically remove defects from a seller's performance evaluation, and the Feedback related to the defect

eBays policy also states:

We automatically remove the defects caused by the reasons listed here. Sellers may request the removal of these types of defects if they are not automatically removed.

• An eBay Money Back Guarantee or PayPal Buyer Protection case is ruled in the seller's favour.