You paid for delivery to your door. You have no contract with USPS, you have one with the seller. If the seller choses to use USPS because it's cheaper that's

You paid for delivery to your door. You have no contract with USPS, you have one with the seller. If the seller choses to use USPS because it's cheaper that's on them. You can get your money back. That said, it shouldn't happen in the first place.