unable to view/change plan online

I need help!

I contacted CS in Oct to lower my bill.  For whatever reason, no one seems to be allowed to change or manage their plan online.  The rep said that there were upcoming specials for both new and existing customers and that I should wait and call back in a few weeks.  She went over my bill and said that I was in an old plan that no longer exists and I was definitely paying too much money.  She went over the various plans and said she could practically cut my bill in half, (currently paying around $300) while improving my internet, currently 400Mbps to 800 or even 1200.  Excited about the savings, I waited.  I called back and the gentleman I spoke with also said that I could save “big” but I had to call back as the specials weren’t available yet.  Finally, I call back and explained to the woman the several convos that I had about saving big bucks she said the specials were for new customers only.  I said that’s not what I was told twice.  She said let me look at your bill.  She went over my bill and >>>  she offered to eliminate ALL of my premium channels and save me $20 a month <<<  Are you kidding me?  Pissed, if it was only me I had to consider, I’d have cut the cord completely.  Right then and there, I’d have told her to cancel my account and not even bother sending me to the retention department.  BUT, I care for my elderly mother and she’d have no idea how to stream.  I did look into Verizon, for better internet, more channels and regular phone service, I can save over $100 a month but again, I don’t think my mother could find her channels.  If I can’t significantly lower my bill, she’ll have to figure it out.  Can you please help me?  Why is it that you don’t offer savings to existing customers?  My Xfinity bill is about $400 a month between cable, internet, phone and mobile.  I can’t sustain that.