If you've purchased your D-ticket through the Deutschlandticket module, it's a one-time purchase, and the subscription will automatically renew each month unless you choose to cancel it.
If you cancel your ticket before the 10th of the month, the cancellation will be processed by the end of that same month.
However, cancellations made after the 10th of the month will be addressed by the end of the following month, in accordance with the Deutschland Ticket policy.