Hi Martijn,
Before moving on, I want to confirm with you first.
1. Do you mean that you could login Microsoft Online Portal (MOP) and click the Team Site link, you couldn’t access the Team Site?
2. Could you access the Team Site before?
3. Have you ever change your Office 365 account domain or others?
As I understand, you can’t access the Team Site.
Currently, I suggest you create another global administrator to see if the issue persists.
Moreover, could you please use other browsers or other computers to see if it works?
In additional, could you please provide the error message when click Team Site link in the MOP for further troubleshooting?
Thanks,
Eric Sun