The comment must have included something which breached feedback rules or the law in some way (you can't just write whatever you like in public feedback). If you can remember exactly what you wrote, word for word, someone will be able to tell you where you went wrong. In the meantime, check out Ebay's feedback rules (in the Help pages with their integral search - links at top and foot of any page).
I'm not sure how the seller managed to make a simple return 'a living hell'. All you have to do is open a case or return request and follow Ebay's instructions. There is no need to get into any communication with the seller at all.
@thewiveskitchen1951
