Why does my mobile data work for some things?

I'm not really sure when this started but I've discovered that I have some type of data. My parents haven't included data in my line yet I'm able to receive notifications from discord, youtube, google feeds etc. I can even do google searches or search for apps on the play store. But I cant actually go on a website or install an app. I cant watch youtube videos or read my discord messages. I cant play online games like brawl stars because it wont connect to the server. I can also use google maps and read reviews. My service provider is tmobile btw. Why does my mobile data work for certain things but not others?