Why is my bill raising from $40 to $100 after one year and no changes to my plan?

I am a student who signed up for Xfinity last September. I got a deal in which I paid $40 a month for Xfinity wifi. All of a sudden, my bill has been raised to $100. And in my other ticket, you will notice that my wifi has been terribly slow despite Xinifty claiming my connection is strong. I don’t want to pay so much more when my wifi barely works at it is.