Anecdata, they might have had a system error. My Microsoft account that I use the free tier OneDrive on had the same email sent (you're over x% full, consider upgrading!). I suspected everything you did - eventually I logged in after verifying the email - nope, 5% usage or so.

I then went and deleted more stuff, but my money would be on a reporting glitch than a malicious money campaign.

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cachius 5 hours ago | parent [-]

A system error on a file storage system makes it even worse! But easy to imagine after the recent report on Azure https://news.ycombinator.com/item?id=47616242

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wallstop 5 hours ago | parent [-]

Sorry, what I meant by "system error" was more "notification system error". Not error as in "data loss", error as in "reporting".

	▲	manwe150 4 hours ago \| parent [-]
		Myself–and many redditors–got this erroneous notification too. I don't think Microsoft ever sent out an "Oops, sorry, you don't actually need to pay us" correction though.