um is it your router? try going to 192.168.1.1 and have a look around a page that should be named something like "Blocked"
ok, what is the isp? read their TOU/EULA whatever the hell they have and see if it states that they do this. If they dont state it ring em up and ask whats up.
read your isps terms and conditions. If it does not state it filters out sites then you can ring em up and ask them whats doin. Even if it is stated ask why they do it anyway.
ok these jokes dont help. my mom does not care about gfx. dont post about my. post possible solutions