Can't log in to xFi on my iPhone8

I keep getting a message about "active time".  When I try to log in to Xfinity on my iPhone (for the very first time), I get a message that I should use xfinity.com to log in.  I checked OK.  When I put in my xfinity username and password, I entered the xfinity.com username and password, which works on my PC.  I get a message that my username or password is incorrect.  How do I log in?