Buyer requested a return but I haven't recieved the item back

I sold an item of used clothing on Ebay and a few days after posting it the buyer contacted me to say that it smelt musty and was unwearable. It was freshly laundered and I didn't notice any smell when I packaged it up but I decided to give them the benefit of the doubt and offered a full refund including return postage. I sent them a prepaid return postage label (not recorded because the value of the item was pretty low) on the same day as they contacted me but now 3 weeks later I haven't received the item back and I haven't heard anything else from the buyer. I contacted them about a week after sending the postage label to check when they sent it but didn't receive a response. What should I do now? The buyer didn't open a SNAD case but all messages about the item have been sent through Ebay.