How can I cancel the Deutschland ticket?
You always cancel the "Deutschland-Ticket" with the provider.

The provider is your contractual partner for the "Deutschland-Ticket", not billyard!
Termination at DSW21 (Dortmunder Stadtwerke)

With the provider DWS21, you may terminate a subscription until the last day of a month.

Information from DSW21: If the termination is carried out only a few days before the end of the month, due to procedural reasons, direct debit may still take place for the next month. The amount will then be refunded to you.