EBay has a Resolution Centre at the bottom of this page for member to member disputes.
Pitney Bowes runs the Global Shipping Program (GSP) for eBay. If the problem was with delivery or with damage in transit, start with the eBay Resolution Centre and state that this is a GSP problem and that you need a GSP specialist.
If your GSP parcel is later than you expect or you just want to track it : use the UPAA number you were given here:
https://parceltracking.pb.com/app/#/dashboard/
Vaguebooking doesn't get answers.
If you have an actual problem, post it here and you can get advice from experienced members and occasionally from eBay employees.
