This number is constantly calling my grandma, 5x a day. Always the same thing. "Trying to save you money" on electric bill. Grandma boarder line cusses them out and they still won't give up.

First stop answering since that only encourages them.  Second:
Call Blocker
You need to buy a standalone call blocker, call blocking phone, use your carrier’s call blocker if they offer one, or download a free call blocking app for smart phones.  For conventional cell phones, assign the number a letter like “z” and make no ring.  You may also need to have your carrier increase the ring time to avoid having them leave a message on your voice mail.