866-874-8380 is the VERIZON CUSTOMER LOYALTY DEPARTMENT - NOT a SPAM call.
When this call came in, it was marked as "spam" by my `Mr. Number` app. (BTW, a great app!) I decided to answer it anyway, and it found it was a nice guy calling from Verizon's Customer Loyalty Dept. That department alerts customers if they're over-spending for services that they are not using. Apparently, I was using very little data on my plan, so he gave me a credit for non-usage, and lowered my data plan to match my usage, saving me about $300 annually.
His call also gave me a chance to discuss some issues that we were experiencing with their Delphi and Sure Response devices. They will give me a credit for some of the problems, and will replace the devices.
So, if you have Verizon, put this number in your contacts. I think you will be glad you did.