International order shipping

I have an order from Europe and I shipped via ebay international shipping, the order was made Nov 17 and I shipped the next day. Today, customer is asking me if I ever shipped the package because the tracking is invalid. I checked the USPS tracking to ebay warehouse and it was recieved there.

Customer is asking if I even sent the package and which I did but ebay hasn't sent it and it's already been a more than a month. Any advice on how I should I proceed and reply?