Upgrade from a First Class label to a Priority shipping label

[nwyr114]

I received an item that needs to be returned; however when I printed the return label and took it to the PO it couldn't be used because the item (scooter) weighed over 13oz, so I messaged the seller for an upgrade to a Priority label but I'm unable to get a response from the seller, and because eBay now has such no/poor customer service you're also unable to get them on the phone, and there's no drop down menu for this problem or any solutions given, this is why not having  live customer service shouldn't be allowed. What is happening to America.