Return aftr closed case

I sold a phone and 4 days after delivery they emailed to say they wanted to return it as it was faulty (perfectly fine when sent it out) so I sent a label for return. The next morning eBay emailed to say the return was closed and I didn’t need to do anything. I’ve noticed today that the item was still sent out and was apparently delivered to me on the 27th March. I have not received a phone. I’ve reached out to eBay and had numerous messages saying parcel was delivered, then courier must of lost it etc etc and they I still didn’t need to refund. So do I actually need to do anything. I tried to message buyer but it says they have been suspended. I’m just worried they may do a chargeback through bank am I covered if they do. I tried to contact Royal Mail about lost parcel but it says it needs to be done from the senders end but obviously can’t get in touch with them. Can anyone advise or help please?