The new Deutschlandticket is a subscription that must be cancelled in good time. You have to cancel the ticket by the 10th of each month.
If you don't cancel by then, you'll pay more for the ticket. The exact cancellation procedures may differ from provider to provider. At Deutsche Bahn, they proceed as follows: The most direct way to cancel is via the subscription portal under https://abo.bahn.de/portal/#/. You can then select which subscription you want to edit or cancel.