Hi Wim,
To troubleshoot the problem, I’d like to confirm the following information:
1. Do you have another admin account can access Office 365?
2. Which domain you’d like to remove from Office 365, the tenant domain as domain.sharepoint.com or your custom domain which is ever verified in Office 365?
If the trial has expired, users are unable to access the expired subscription. To remove the tenant domain and cancel the subscription, please contact our sales and billing team referring to the link below:
onlinehelp.microsoft.com/.../gg570308.aspx
Thanks,
Nancy Xie