Welcome to the forum. The meter is not a real-time counter; it's updated once a day at 23.59 and even then the figure doesn't appear until later in the morning. That makes it useless for indicating usage during individual operations.
If you're downloading video it's probably best to pay an extra fiver a month (or whatever it is) for unlimited. Not only would that end the chance of unintentional overuse, it would allow you to download to your heart's content.
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