It’s easier to pretend your data were deleted than collecting part of your data and sending them back to you.
They almost every time don’t know how much, where, why they have so much data.
They certainly have no way to collect them, only hand made work, so let’s have a little misunderstanding and hope it works.
Now that you’ve been deleted, wait until you receive the next text or email marketing campaign ;)
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I may or may not be working next door to a data protection officer.
"datum" is the singular, but you're right that it's not really grammatically plural since you'd say "the data was stolen" not "the data were stolen". I think the latter would technically also be valid; my interpretation would be that the latter is "countable" plural, so there are specific discrete datums that were stolen.
Confusingly, British English actually does treat nouns like "data" and "government" as plural where American English does not. Even more confusingly, they're a little inconsistent with it, so you can find published examples of both.