web.de, gmx.net, gmx.de, ... not routed through on comcast network

I've noticed that for a couple of days now that freemailer websites seem to be blocked at/by Comcast.

www.web.de

www.gmx.net

www.gmx.de

I have multiple computers with different OS's (Win7, Ubuntu) as well as Tablets and on all when calling up the websites (whether Firefox, Chrome, etc.) the connection times out as unreachable for these specific websites. All other websites seem to be working fine.

When I connect to the same websites through Verizon network, through my work network (which is not-Comcast), they all load up without a problem.

Any statement from the experts ?

Has anybody seen the same and resolved this somehow ?

Any suggestion on escalation? If this turns out to be true that comcast blocks requests this would be censorship at the most serious level.

Regards

FD