web browser restriction - off wifi - safe page

Hello, has anyone else had a problem with a website that is safe (I've been using this website since middle school (2013)) not working when off wifi? 

For background info, this website is a place were i read mangas or webtoons and it has been a safe website IMO (never had issues). I've notice for a while that it doesn't work when I disconnect from wifi. I usually just let it go but now it gets frustrating as it's a relaxing space to go to when my son is asleep.

I went into incognito to see if it would work there but it still didn't work. But something new popped up that I've never seen before (as I've never tried this) and it said this: "Content filtering has been enabled on this line and is restricting your access to this content. An authorized person on your account may be able to disable this restriction through the account management website"

Can anyone help me figure at what to do? (I've been on this line since middle school so idk if the restrictions have been updated but I'm sure they have)