Thanks for your answer. I am sorry but Mobile usage says:
No mobile usage data collected
for Day, Week and Month and for Total there is
Total usage *: 19.31 MB
Sent *: 1.49 MB
Received *: 17.82 MB
I know that yesterday it was over 9 GB, so the information is very inaccurate, I have no idea what it counts.
Although if it collects data properly, it won't send SMS and the interval for collecting could not be set (I have 16.7. - 16.8.). I would recommend to modify the behavior of Data usage not to be reset after the reboot.