Where is the buyer located? Does the tracking show that the package was refused?
I don't know how it works in other countries but in Canada a gsp package gets sent from Kentucky to a hub in Canada. If a package is refused, the return address is the Canadian hub so apparently a return to sender package would go there, not to Kentucky. Based on other posts I've read, the package is then untraceable or at least the gsp doesn't give out any info about it. I find it odd that a package would go back to the US rather than the hub in the other country.
Generally if a buyer refuses a package or if it shows return to sender, the buyer is not covered by the MBG because the item was delivered. The same is true for the gsp.
