Wifi is what you connect to a router with. I suspect you are looking for mobile data and your query would be better suited in the mobile devices and apps subforum here:
https://aseannow.com/forum/146-mobile-devices-and-apps/
Or have a look at similar threads in that area.
Regarding the issue with your current package, you should be able to check what you've bought in the app, and contact DTAC if there's a problem.