Hi,
Not sure what is your current configuration, but I assume you're using Authentication mode: Without Radius, which will allow you to put data/speed limit to the whole created user, but not to individual WiFi users.
If your goal is to limit each WiFi user's data consumption, you should tried using Authentication mode: MAC auth, which will put data restricts based on the users MAC addresses, that way each user will be limited to data, that you set.
Using MAC auth you can also enable password protection, so that unwanted users will not be able to connect to your Hotspot.
You can add data restrictions in Session Settings section.