keeps calling at odds times and days of the week

This number has called me three times over the past week, at 11:15pm, 1:30am and 5:30am.  The calls are to a cell phone.  I tried calling back today to ask them to stop, but got a message saying the number is not in service, so caller ID is probably spoofed, or the number doesn't accept incoming calls.  Really don't appreciate being awakened by these idiots.

Received calls on business cell phone just after midnight CDT on 09, 10, and 11 Aug, and also 11:00 CDT on 11 Aug.  Silence on the other end.  When I tried calling back, I received a message that the international call I was trying to make is not permitted on my line.  Strange, since multiple websites show this area code to be in the Memphis, Tennessee area.

I talked to AT&T customer service and they tried calling the number, and got a busy signal.  On personal lines there is an option to block calls from certain numbers, but business lines do not have this.  AT&T did some queries but was unable to find out anything further about this line.  They suggest making sure your line is on the do-not-call list (http://donotcall.gov).

@chicagoland, They only tell you to check if your on the do not call list because its the only answer they can think of....i agree with spoofed phone numbers...its very easy to do.

Called work cell two times this week during middle of the night.