[Pyramids]

Although it'd be hard to ever answer this definitively, I've personally had this happen due to overly aggressive fraud detection systems.

In my case, my cable modem was assigned an IP address from a "new" pool which had not been picked up by geolocation companies (MaxMind) and as such, my order was scored very high and automatically canceled.

Again, the only reason I have this knowledge was because someone working at United was friendly and upfront enough to let me know what the issues were, so in your case if you didn't get any information, it'd be hard to determine.