I have had 4 buyers from 4 different locations buy the same product and then say they haven't received my item and requesting a refund, what should I do? I suspect it's a scam.

I have tried reporting the buyer but there's no option for stating non delivery and wanting a refund.

I have tried asking ebay to step in but can't find the option to do that.

I have proof from each delivery that it's been received at the right address.