I got one the 24 of Dec. at 10:30 P.M. I just got one more at 2:15 P.M. today. Each time there was only one ring.
This is one of the "Grenada (area code 473)" scams.
They call late at night and only let the phone ring once.
They want you to call them back.
When you do that, you could be hit with a phone bill with a large international calling charge. These scammers will get a cut of those charges.