Xfinity Deceptive practices

How can I get my bill to reflect what I believe I signed up for.  In August, I called Comcast to sign up for Internet with a $25/month promotion and including the modem -- for new customers.  When they came to install the cable, they found our house was too far from the street.  It took Comcast several months to get the high speed cable connected to the house.  Once that was done, they connected us to internet -- for a cost of $35/month, plus $15/month for the modem. Got my first full month bill yesterday.   My internet cost had doubled!  When I agreed to the price, I asked the person on the phone if I would still get the original deal -- she said she put a ticket in my file as assured me I would get the original pricing.   Yesterday, the agent told me that I was out of luck.  That price isn't available.  I feel that this was all very deceptive. I am ready to return to AT&T since the reason I switched was cost.  How can I get back to the cost I signed up for?  And, if I go back to AT&T, how long do I have to wait until I am a "new customer" again?