Service cancelled or not?

juergent 

I am sorry to hear about your experience with the mail transfer not working out with Microsoft. If you are unsure if you have canceled your account, you can try logging into your account by navigating to Microsoft 365 Admin Center. You must be a Global Administrator or have the appropriate administration access. You can learn more about Administrator roles here: About admin roles in the Microsoft 365 admin center - Microsoft 365 admin | Microsoft Learn. You will want to stop billing to occur with your account. Then cancel your subscription. 

DISCLAIMER

Make sure you have fully migrated your data from OneDrive, SharePoint, and Exchange before proceeding with the following steps. If you have other accounts that may have data, such as employees, please see: Step 2 - Save the contents of a former employee's mailbox - Microsoft 365 admin | Microsoft Learn. You can also contact support with your previous support ticket number for confirmation. Then cancel your subscription. Please follow the instructions below:

Turnoff Reoccurring Billing

1. Login into Microsoft 365 Admin Center: https://admin.microsoft.com.
2. In the left-hand menu select the Billing tab, then select Your Products.
3. Select the products that you want to close your billing.
4. Under "Bill settings" section, Edit recurring billing.
5. Select off, then click Save.

Cancel Subscription

1. While in the Admin Center select the Billing Tab in the left-hand menu, then Your products.
2. Select the product, then go the Billing settings section, select Cancel subscription.
3. You will be able to cancel your subscription based on your preference now or the next billing cycle.

Your account should now be effectively cancelled. I hope that this information was helpful.