24 Months rate agreement being changed after one year

Hello,

 One year ago I siged up for a 24 Month agreement to specifically lock in a rate of $60 month taking advantage of a promotional discount of $20 on my initial plan, plus another $10 for autopay and $10 for paperless billing. Today, while checking my account, I noticed that I was charged $80 instead for the month of Septempber but also billed $80 for October. I called Xfinity billing to inquire about the change in procing, and regardless of what the rep was saying to justify the increase it never made any sense to me. We talked for almost 1 hour without reacing a resolution that satisfies me, which is to remain on the $60 monthly payment. I asked to talk to a supervisor but the rep tells me there are no available supervisor right now but will hopefully get someone to call me in 2 hours. I am utterly  disappointed by yet another bait and switch by Xfinity. YOu signed up for a 2 years contract that carries a max fine of $230 fine should I decide to exit the contract but Xfinity has all the latitude to not only change my plan, increase m monthly payment without my knowledge or conscent. I am not sure if I will get a call back but I am hoping that someone could explain to me what a 24 month agreement really means for Xfinity???