Worst experience ever!!!!

We have been a customer with Xfinity /Comcast for 20+ years with steadily increasing rates. Recently we have had issues with our cable box, so I decided to take it to the Xfinity store and swap it out - sounds easy, right? Two trips to the store 30 mins one way, I still do not have a working box. The fist box they gave me was a “flex box” that is apparently not intended for the services we have. The second box required me to contact Xfinity at a specified number to activate. Of course you can’t talk to a live person without standing on your head. Well I chat (text) with someone who says I have to approve the activation by email. I do this only to find out that this approval granted them permission to change my grandfathered plan to a more expensive plan with less perks. I was livid and spent hours on the phone with customer service. When I asked for a supervisor, I was told they would call me back - didn’t happen. Called again and they offered me a $15 credit for my trouble, directing me back to the store to get me issue resolved b/c there is nothing else they ca. do about it. Are you serious? You [Edited: "Language"] and it becomes my problem? I need someone to help me fix this error!