Rubbish, it happens regularly with all sorts of companies, all over the world.

Just a couple from personal experience,  I had a standing fortnightly order with an Australian company,  it took nearly 12 months to receive an invoice, all payable within 30 days.  Invoice was correct and duly paid.

Opened a  telecommunications account with a fledgling Australian company, with invoices due monthly, six months down the track no invoices received  and the company ceased trading.  Several months later was contacted by debt collectors, with a demand for payment,  returned serve with a demand for a copy of all invoices  issued to verify the debt.  Next contact from debt collectors was to advise that detailed invoices were not available and the debt was subsequently wiped.

I do not use ebay labels, but surely it can not be too difficult to reconcile  what has been paid for and what has not and if you have  incurred the costs it is time to pay up.

Just a tip if the unpaid charges finish up in the hands of a debt collector, the debt will automatically balloon.