need help! turn off Voicemail & stop marking an important phone # as spam

Please don't just tell me to set # of rings. I want to completely turn off Xfinity voicemail option on my VOIP phone. Further, I absolutely need to make sure this specific phone number is NOT identified as medium spam risk and is put through to my phone, please: [Edited: "Personal Information"]

This is an emergency alert # that is to inform me of tornados active shooters, etc.