When I answered the phone, it was an automated message, asking me to call of 866-750-3446, in reference to an outstanding bill. Instead, I called the number that called me (480-222-3446), rather than the 866#.

They are a debt collector. Most likely representing more than one company and probably for a medical bill of some sort.
In my case, they were representing Gilbert Hospital. I selected 0, when given the option to speak with someone right away. The girl that answered was nice, but NOT professional. I told her they called my home number (gave her the number), she looked it up and said, "Oh, Gawd, soooooo sorry... You're totally cool & it's all good... I see you already paid this bill. Not sure why our crappy service called you. Go ahead and disregard the call. You balance has already been paid in full".

I thought to myself, "WOW!", chuckled and we ended the call.