In my post, I said this just happened yesterday, and a few times within a month. I don't know why people are telling me how good Prime has been to them. They've been good to me too.
But never did they do something like give me a delivery date for the 4th, take my money, then change it to a later delivery date, until recently. The first time this happened, they offer delivery the next day on the 10th, took my order, then immediately changed my delivery date to the 15th. I almost cancelled the order.