Install from app store DNS channger app, and enter 8.8.8.8 and 8.8.4.4 and see will it work on wifi.
How is 3 filtering your adult content on the phone? I bet through some proxy on 4G connectio. Meaning all your 4G traffic goes through their filters.
Anyway 3 has nothing to do with Wifi, so try the DNS change, though it seems thats useless too since you tired it on another wifi not on same ISP of your home.