Hi Cristina Zanetti,
Thank you for reaching out to the Microsoft Q&A community.
I understand that you're incredibly in need of your BitLocker key. I wish I could share good news, but I have to be direct: no one can give you that, not even Microsoft.
The key is often saved to the very first Microsoft account used to set up the computer. So let's look for it one more time by visiting the official Recovery key page. Sign in with every possible account you or others may have used on the PC (personal, secondary personal, work, school, etc.)
For work or school devices, you can also ask your organization's IT department in case it was in their library. Also check in OneDrive cloud to see if there's a chance that the key was automatically saved (look for any .txt files mentioning key / bitlocker)
If you can't find it at all or it was never backed up, it is impossible for Microsoft to send you BitLocker key. I know this is not the answer you were hoping for, and I'm sorry to have to share this difficult information. But I believe it is best to be direct and give you the correct information.
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