eBay Seller of 10+ Years Files a Complaint Against eBay Sellers Program

Found so many complaints about eBay sellers, I was quite perplexed filing this as a seller. I was indeed a 10yrs+ seller on eBay and still work so hard to please my customers (they ones who provide me a needed 2nd income, no matter how small it is). Recently I made a mistake & sent a wrong item to a Buyer, and was notified by eBay a few days after delivery about his request to return it.

After checking my stock & records, and realized of my mistake I approved his requested and generated a prepaid shipping label through eBay return/refund system, also email him explaining & apologizing about the mistake with the promise of resend the (correct) item at .my own expense.

Our communication didn't stop there as he kept complaining about the "not-as described" item he received, and at a certain point insinuated that I sent him the wrong item on a purpose (that it was floating around for months on different e-commerce sites without anyone wanting it). 

I didn't list this item on any site except eBay, and despite my (again) explanation that the mistake was un-intentional, and obviously the original description referred to the (correct & unsent) item he had not yet received & examined. He abruptly closed the return request, and left a negative feedback for me with comments about bad description on the substitute item, and have to pay for postage to return it. 

I've contacted eBay Customer Service attempting to remove this online negative feedback (amongst my thousand+ Positive ones, it brought my ratings down to 96% from 100%, as I didn't made to many sales in the last quarter), my request was denied by several reps on the ground that it was a buyer's right to express his/her own "feeling" about a transaction, and that I - as a seller - had made mistake and should learn something from it (sic).

As anyone can see, the feedback content was not about a "feeling" but a blatantly false statement against the truth that we - ALL the involved parties: myself, the buyer, eBay) - knew untrue, with the sole malice to hurt my reputation possibly from a competitor? 

I'm at my wit end as what to do at this point, for too long I knew eBay's "Seller Protection" policy was just a joke, and their Customer Service only built on a bunch of non-native English spoken personals (s a foreigner I have problems understanding them myself besides their "canned' responses), but I'm still a seller as there're still 1000' other "good" buyers as bad sellers (of an equal #/ I hope not!) out there as well.

I guess I've just paid my overdue painful part, though eBay corporate headquarters and the level of service they allow is getting worse everyday.