There are many factors that cause data consumption. The phone itself will not actively consume data but only when the relevant software needs to run. It is recommended that you confirm the details of the charges with the operator for the specific reasons of the charges.
It is recommended that you refer to the following solutions:
1. Settings > SIM card & mobile data > Data usage > Set Mobile data limit.
2. Settings > SIM card & mobile data > Data usage> App network permissions - Turn off unnecessary mobile data permissions for third-party apps to avoid extra data generated by malicious third-party apps.
3. Settings > SIM card & mobile data > Turn off Use Internet during calls on secondary data SIM
4. Turn off the VolTE function of the secondary card.
5. Turn off the MMS function of the current non-Internet card, and MMS will generate data consumption.
6. Go to developer options - turn off Always keep mobile data active.
7. You can contact the operator to turn off the Internet access function of the secondary card.
