If an item is not as described then you do not need to contact the seller you just open a dispute My item is not as described. You do that by going to the item in your sold section or ebay help at the top of the page
It is all automated. The seller sends a pre paid label for the return and once they have it back then they refund in full. If they dont then you go back to the dispute and escalate to ebay who will force the refund.
It is not really good just to leave feedback when you have a problem. All those sellers left you positives.
You dont have to remove/ change the feedback unless you are happy with the way the seller deals with the problem.
See the link to the ebay money back guarantee
https://pages.ebay.co.uk/ebay-money-back-guarantee/
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We are just ordinary members trying to help.