Mercari complaint: never received my package

The seller according to USPS sent my 14 years old son’s package to a different address the seller did not use the address my son provided. Mercari says that because the USPS tracking number said it has arrive to its destination they refuse to refund my son the $332.77.

Yet on their website when using that same tracking number it says : address not found therefore package was not able to be delivered.I am his mom and I personally talked to the manager of USPS and they can prove that the package has never been delivered to our address. Mercari is not responding anymore after sending a message saying that they will not refund us the money.

They also blocked us from directly messaging the seller even though my son messaged him 2 weeks ago but never heard from him.My 14 years old son has been scammed, today is january 4th and he bought the lego box on Dec 22 2022