Ebay won't remove negative feedback with customer consent!

[easy.t3ch]

I have this customer who left a negative feedback on a moment of anger. 

I'll try to keep it short but would appreciate any input.

The customer is not using ebay platform too much. After he left the negative feedback for a wifi dongle which didn't work on win xp as plug-and-play, mentioned on the listing that it works only on win 10 and for other platforms a small driver is required. 

Anyhow, issue sorted, customer very happy, messages were sent back and forth on period of 6 months. Feedback revision sent and expired because he didn't see it on time. 

I sent him a message if he accepts ebay to remove the feedback for him and he was happy for ebay to do so as he is happy with our support. This were instructions received from ebay support and then once customer accepts to call them back and they will remove it. 

I called back and all message trails are on ebay, they said they are not allowed to remove the feedback as that is what customer thought of the product. 

Has anyone else had similar issues? What can I do?

[plpmr]

adding to the advice already given -

Plus the fact that "Feedback revision sent and expired because he didn't see it on time" - expired and you only get one per feedback.