Received 3 calls from this number over past 2 days. Each time I answered the call hung up immediately. I called back the number. A robot answerer gives you the option to no longer receive calls from HGVC. If you select that option (2) the call is promptly answered by a polie human who adds your number to their do-not-call list, no questions asked. They are a reputable business and probably have your number through some sort of a legitimate business relationship (past stay at a Hilton property, membership in a vacation club or timeshare with which they are affiliated, etc.).
Got a missed call on my cell phone this evening. Out of the blue decided to punch the number into the internet browser and see what came up. Becuase I did not recognize the number and they did not leave a message.