Oppo
Set Data Usage Billing Cycle Start Date auf Oppo
Oppo phones running Coloros track mobile data usage in monthly blocks that reset on the 1st by default. If your carrier bills you on a different date, the on-device usage counter and your actual invoice never line up, which makes it hard to judge how close you are to your data limit.
The fix is in the mobile data limit settings, where you can set a custom start date for the usage stats. Once changed, the counter resets on that day each month instead of the 1st, matching your real billing cycle.
Open Settings ➔ SIM card & mobile data ➔ Data usage ➔ Mobile data limit ➔ Start date for data usage stats. Pick the day your billing cycle actually starts, then confirm with Save.
This setting only changes when the counter resets, not how data is measured. If you mainly want a warning before hitting your plan limit, set the data limit value in the same menu instead of just adjusting the date.