Internet speed plan changed without my consent!

I originally signed up for the 600 Mbps internet service for $45 per month for the first year. After just over six months, I checked my bill and noticed that my internet speed had been changed to 1 Gbps, and my monthly bill increased to $70. I did not request or authorize any upgrade to my service.

What I’m understanding from this is that—even before the first year ends—Xfinity can change and add services without customer authorization and expect customers to pay for them. It would have been appropriate to receive a notice at the very least, but instead it feels like the change was made quietly in hopes that I wouldn’t notice.