You should have been informed of the price increase before it occurred, and been given the option of leaving penalty free. There are lots of posts on here where people have either not seen or not received the email. (which would have been from Sky)
Call Now and try to renegotiate a new contract.
To follow-up from @Jayach
The broadband team number in this link. Make sure you're signed in otherwise you won't get to see it.