Yes, it is Charter. I also have only internet from them and they want me to bundle. They are not subject to the conditions of the "Do Not Call List" since I am already a customer. I answered thinking it may be someone I know since I am originally from Missouri and recognized the area code.
I too have Internet only. Have a spam filter in place. They call from this plus another toll free number. Stats show that I get at least 6 calls a day from them and sometimes 8 a day on weekends.