If you use your phone's data all the time, you're a heavy user. Then, if you use Discord a lot, it could sometimes use up all of your mobile data. But there are some things you can do to stop this from happening. One of these is to turn off the setting that lets you preview links. This will make sure that the user doesn't automatically download the links or images that are sent to them.
You can also set a limit on the amount of data your app can use. This will turn off your mobile data once your input amount has been used up. Don't forget that this setting doesn't just work for one app. The bandwidth limit keeps track of all the data your device uses, so it could turn off your mobile data even if you're using another app. You can get around this by switching your internet package to one with more bandwidth.