I, too, received am early morning call from the aforementioned number. Attempt to call back was fruitless: "Your call cannot be completed as dialed..."
Any advice on how to stop these unsolicited calls is greatly appreciated.
There's no way to stop the calls from being initiated. Invest in a call blocker and DO NOT pick up on call numbers you do not recognize. I realize that's difficult if you are running a business.
I got this call blocker 5 years ago best $5.99 I have ever spent. (Think it may be $6.99 now but well woth every penny) It will allow you to block any numbers you want, also you can have it just hang up on the caller. The app is called Extreme Call Blocker...