Hi @Pierre MARTIN ,
Welcome to our forum!
Please kindly understand that the Outlook tag here we mainly focus on general issues about Outlook desktop client. Based on my research, i found that we can refer to this article to recover a hacked or compromised Microsoft account: How to recover a hacked or compromised Microsoft account.
If you are using an Outlook.com, it's suggested that you could post your case in dedicated forum for Outlook.com for more professional advice.
Hope to help you!
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