I had a very simular experience, the Comcast store close to me has issues as well, every time I leave there my next bill mysteriously rises! In my opinion though I dont think that it warrents "cutting the cord", I didnt despite the frustration.
Sorry for the experience you had while trying to have the box replaced. If you have not received help getting the box activated, please send me a private message verifying your first and last name, the phone number, street address including city state and zip code, and the account number associated with your services.
Thanks for reaching out. I'm sorry to hear about your billing concerns after leaving your local Comcast service center. If you'd like me to review your account to see if there's any way I can assist you, please feel free to reach out in a private message.
To send a private message click on my name "ComcastChe", then click private message me.