Looks like the case closed because you ran out of time to receive the correct return label to send the item back.
If a seller issues the wrong return label it's usually a 2kg one unless the seller adjusts this to show the correct weight, what you should do is to contact eBay Customer Services who will re issue the correct label, and charge it to the seller's account.
If the timeframe for this has lapsed, then you cannot reopen a case with eBay and now, need to turn to your payment provider for help with your refund.
@rdewdney