So far each time I ordered something I got it. I don't even imagine how in your situation I would have to prove that I did not get the delivery. If it is possible I order things to be delivered to home but few times I had to pick my order from delivery box as well. First time I was entering the right numbers but nothing was happening. Only after a while did I figure that I had to touch the screen first.
Sone of the apps and screens are not very intuitively designed.