Yes, I did a check and it says 406.93MB used 
But one thing I noticed is that I accidentally left my phone on (playing music) before bedtime and the warning SMS was sent around 5am. But I didn't turn on mobile data before I go the bed. I did turn off my home Wifi though.
Could the music or some other apps in the background automatically switched to use mobile data when WiFi was off?
Even then, the Redmi note 3 should reflect the actual usage, isn't it? (*puzzled*) Don't know if it's M1 or RN3's problem now.
But one thing I noticed is that I accidentally left my phone on (playing music) before bedtime and the warning SMS was sent around 5am. But I didn't turn on mobile data before I go the bed. I did turn off my home Wifi though.
Could the music or some other apps in the background automatically switched to use mobile data when WiFi was off?
Even then, the Redmi note 3 should reflect the actual usage, isn't it? (*puzzled*) Don't know if it's M1 or RN3's problem now.