Unless Recorded or Registered mail was used, which covers for any loss in transit you may have lost your disk.
I have returned 2 faulty titles to ADN, the last one just yesterday and make a point of using Recorded delivery to cover the very problem you are facing. If it goes AWOL at least I can claim off the postal service.
As usual ADN Customer Service was excellent and sent me a replacement when they received my return.
If it's any comfort, I have recently experienced losing an order being sent to me from DVDBoxoffice. They sent it by regular mail from Europe although they are a Canadian company and will only consider items lost 8 weeks after shipping. Then they told me they couldn't replace the order. It was an costly lesson at my expense and I will never use them again. It will be ADN for all future orders now even better with UPS tracking.
I hope, things work out for you.
[Link]