Sounds like you left the returns case to time out.
After 3 business days, if the seller doesn't send you a pre-paid returns label you can escalate it to eBay and there'll be a button asking them to step in, and they'll then issue a label.
If you just leave it, and don't escalate it, after 30 days eBay will assume that you're no longer interested in pursuing the claim and the case will automatically close.
Once closed, a case can't be re-opened and you can't open another for the same transaction.