Managing personal Outlook.com account settings, security, and privacy
Regarding the Dutch advertisements, seeing ads in a different language does not necessarily mean someone still has access to your account. Advertising content can be influenced by regional preferences, browser cookies, and previously collected information. To better understand what's happening, could you please clarify a few details?
Are only the advertisements appearing in Dutch, or are parts of Outlook's interface also displaying Dutch? Are the Dutch-language emails coming from unfamiliar senders, or are they advertisements from companies you previously received messages from? Does this happen in different browsers, or only in the browser you normally use?
Open your browser in an InPrivate or Incognito window, sign in to https://outlook.live.com, and check whether the advertisements still appear in Dutch. If they appear in English in the private window, the behavior could be related to stored browser data or cookies rather than an ongoing account compromise.
Please share your findings. Since your account was recently compromised, I would also recommend avoiding links in unexpected advertising emails until you're confident they are legitimate.