I had something similar happen with UPS recently. They were supposed to deliver something 3 days in a row, and every day their website said it was on a truck for delivery. They usually come about 8:00 PM, so I think I must be at the end of their route, and the driver probably fell behind and didn't make it my neighborhood all those days. What was especially annoying was that it was a SurePost package that should have been delivered to the Post Office for final delivery, but UPS said that they were going to be in the neighborhood so they'd deliver it themselves.
FedEx is worse, in my experience, in living up to when they say something will be delivered. They will deliver a package early, though, if they have it, which UPS will never do. UPS will let it sit in a truck at their facility for two days if the delivery date hasn't come yet.
I'm up to two months now waiting for a set of keycaps from AliExpress. They say it was finally dispatched from somewhere in California two days ago, so at least it's in the US, although not with the Post Office or through customs yet.