why does mobile hotspot take up so much data even though i turned hotspot

• If you use an Exchange ActiveSync account, it might continue to use cellular data even if you turn it off for Mail and Calendar. To see the cellular data usage of your Exchange ActiveSync account, go to Settings > Cellular > System Services.
• If activated, Wi-Fi Assist automatically switches to use cellular data when Wi-Fi connectivity is poor. Wi-Fi Assist is on by default. This might result in additional cellular data use, which could incur additional charges depending on your data plan. You can turn off Wi-Fi Assist in Settings. For more information, see About Wi-Fi Assist.

How do you know it is daily? It is for the current period.

Please go to Settings > Mobile Data [Scroll Down] And check what is the current period.

If the Current Period is the same as Lifetime then that indicates your Carrier is not updating this current period and hence they are the same.

Lifetime means the time period between today's date and the Last Reset: [Date & Time] (Seen at the bottom of the screen)