Xfinity mobile free unlimited line while purchasing internet with speed 300MBPS+ - is this fake?

I recently purchased internet service from Xfinity with a speed of 300MBPS. While purchasing, the system said that I would get a free unlimited line for a year (while purchasing the internet). This seemed attractive for new customers.

I have stayed with them for almost 50 days with the home internet and the unlimited line (which they said is free).

Indeed, the line doesn't seem free. I am asked to pay 68$ (40$ monthly fee, 25$ activation fee and taxes). 

As you are asking me to pay, this unlimited line doesn't seem free. What other hidden charges are included?