Another dismal experience with these couriers

A dismal experience with these couriers - I sent a package back to Amazon and was notified after I paid that "Please note, you will receive a pdf waybill and Commercial Invoice via email after this transaction". Well, 10 days later I have received nothing and I NEED an invoice to claim the shipping back from Amazon. I contacted customer support and was assured that the transaction had not yet entered the system and would receive a commercial invoice once it had but obviously that has not happened. What sort of a company doesn't issue an invoice even when requested. Some persons on customer care are not up to the job at all and can't understand the simplest queries.