Xfinity makes contracts under one set of prices, then switches mid-contract to a hugely higher pricing. Is that legal?

I agreed to buy Xfinity internet for $39 and the senior mobile phone for $15 (formerly a mint magic customer at $15). In the last two months, Xfinity has

1. Increased internet by an additional 50%. I could not justify this so dropped the internet. At the time, I was told my phone would increase by $10. 

2. Yesterday, Xfinity charged 267% of my contract cost, not $10. Previously $15, now $43 was charged on my Credit card.

I tried to talk to people by phone, but gave up and went into the store to find out how to return the phone. I was told I couldn't. 

Is it legal to change the contract part way through the life of the contract?