How to limit your mobile data usage on Android Oreo 8.0 & 8.1 phones

Steps:
So, From the home page go to "Settings"
Now tap on "Network & Internet"
Tap on "Data usage" and turn on "Mobile Data"
Now tap on " Billing cycle" then "Billing Cycle" again and choose the first day your data package refreshes.
For example my data package gets renewed on the 1st of every month. then tap "Set"
Now i will turn on "Set Data Warning" so my phone will notify me when i approach my limit.
For example i get every month 1 Gigabytes of data, so i will set my Data warning to 800 MegaBytes.
Now i will turn on "Set Data limit" This means the mobile data on my phone will turn off once it reaches the limit i set. tap okay
So i will set my Data limit to 950 Megabytes then tap "set"
By doing this, my phone will warn me once i hits 800 Megabytes of mobile data and disconnects my mobile data once i hits 950 megabytes.