Tom nook all booked up?

The reason for this is because there is a stuck letter in the postal system. The best way to remedy this is to send up to 16-20 letters (usually it takes about 8-10). This will cause the mail to be forced into sending to the recipient(s). You may or may not receive that letter, and if you do, it's probably a letter you would recognize, like a catalog order. If that doesn't work, try opening the gates to your town and shutting them again. Trying both of these should let you order from the catalog again. I hope this helps.

If you have more than one person living in your house, then you should try to empty all of the mail boxes. The same exact thing happened to me and I tried this and it helped. Sooo, I hope this helps :D

Empty out your mailbox. If your mailbox is full, he won't let you order from the catalog because he can't send you it. If he still doesn't, talk to him again the day after.