Data usage for WhatsApp store automatically in settings. how to get there is very simple. just follow instructions.
open your WhatsApp and open options bar like this
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select "SETTINGS" option like this
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now choose " DATA USAGE " option like this
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Now choose " Network Usage " option like this
now a new window opens up... you can see your whole data usage,
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you can reset your data usage to zero value
just scroll down and click on the option of "RESET STATISTICS"
like this
when you click on the option of reset statistics and click "RESET" like this
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now your data usage statistics will be reset.
thankyou