I ordered a book from Amazon 2 days ago. I jmhace Amazon prime so I have 2 day shipping but my package still hasn't got here. Also on the track my package thing it says it was left in the mailbox at 1 pm but is now the next day? I've looked everywhere and I pretty sure I haven't seen a ups truck for a while? Should I call customer support?

No. I've sorted it out for you. Should arrive tomorrow.

If the tracking says that it was delivered to your mailbox, then USPS delivered it, not UPS. If there is absolutely nothing in your mailbox, then yes, call the USPS about it.

2 day shipping time once it leaves their facilities, which may not happen on the day of the order.

yes contact them. in case you don't know this, you can chat with them too

yes call them