I just received a letter that just says Verizon UVC 500 Technology Dr. Suite 700 Weldon Spring, MO 63304. I'm also not sure if it's legitimate or not?

Did a reverse search on the number 877-462-4792. And it is a legit verizon number.  Called the number.  And it was the Usage Verification Center.  This unit will verify the overseas call made on the account if they appear to be not your customary usage. All you have to do is confirm.  Good idea, since you do not want to be doing the discussion after.  I do agree that the letter does not look legit.  This is what I was worried about in the first place.

Received the same letter today.  It looks like a fraud. It has the verizon logo but on the wrong side of the page and does not say Verizon Wireless like all the letterhead does.

Actually received a letter asking to call 877-462-4792. It identifies the number as  Verizon's the Usage Verification Center.   Do not know if this is legitimate number.