866-665-4386

I just received a phone call from this number. I subscriber to Caller ID and the screen on my phone listed this number as "Potential Spam." So, I followed the instructions. Come to find out, it's my pain management doctor's office using a 3rd party number to confirm my appointment 6 days ahead of schedule - my appointment is next Wednesday. I can handle it myself by calling them the day before, duh. They apparently treat their patients like 5 year old children that think for themselves and need an adult to do the thinking for them.

You've run into the downside of the SPAM designation.  Carriers make this designation based on call volume, user reports and call history.  Unfortunately, and too often, legitimate calls may be ignored because of it.  I had a similar experience with a delivery that required a signature.  The call came in labeled SPAM.  I ignored it and missed the delivery.
Please don't think too harshly of you clinic office.  Medical clinics must book appointments well in advance in order to verify patient information and insurance.  Often, medical offices need to verify your intent to keep an appointment in order to hold your place or make it available to another.