Seeing another person's e-mail inbox in Outlook.com when logging into my account

Hi, not sure if I have found the right place to post this - but after talking to customer support for more than half an hour today, they could not help me as my issue is related to Outlook.com - and I was recommended to try the Tech Community. 

My problem is that I am seeing another person's e-mail inbox in Outlook.com when logging into my account. How is this possible, and how/where should I seek further assistance to solve this issue? I am logging in with my e-