Service Changed Without Permission

I called Xfinity customer service because of trouble with my internet service.  While on the phone with a rep, she suggested I might want to change my service.  I told her to send me a link and I would look at it.  There was a problem getting the link so she asked if I wanted to discuss it verbally. I said okay but we never got to it because of further discussion about the internet problem.  I never accepted a service change.  I later discovered an email that the service had been changed.  When I called to reverse it I was told that the service I had was no longer available because of a "grandfather" exception.  Since I did nothing to forfeit the "grandfather" status, I feel I should be able to return to the service that was wrongly taken from me.  I want my old plan back!