Hi there, @geekhax.
On our bills, online and paper that we send through the mail, we will note that a price change a month before. We also send an email out to notify when your agreement is ending. This is usually the main reason why a bill has increase. I can help look into your account to see what caused the increase and if I can lower the cost for you. Can you please private message me your full name? Thank you for posting to our forums.
To send a private message, please click my name "ComcastMartin" then select "Send a Message" on the right side.