www.comcast.net customer service

www.comcast.net is a site which was used by Comcast to provide internet services to its customers. Later www.comcast.net service was renamed to XFINITY and all services on comcast.net are now redirected to corresponding services on www.xfinity.com domain.
Below is a list of current redirects:

Comcast and XFINITY Customer Support

Comcast could be contacted via chat on https://www.xfinity.com/support/contact-us web page.
Alternatively, you can call Comcast support phone number 1-800-XFINITY (1-800-934-6489)
You can also search forums and see if your issue is described by someone there. Forums are available at http://forums.xfinity.com/