I know this is an older thread, but for anyone searching like I just did for how to cancel the Deutschland Ticket subscription, I appear to have found a new way 😜.
If you use Apple Pay, Google Pay or PayPal as your payment method, the regional transit authority (in my case SSB, Stuttgart Strassenbahnen AG) is unable to charge the payment method for the ongoing subscription. Thus they automatically cancel the subscription. The first payment goes through as authorized by you at the time of purchase. Then their system automatically unsubscribes you immediately for future months and sends a cancellation email. No muss, no fuss. I've carefully read all the emails and checked the app (I used VVS Mobil, the regional transit authority for Stuttgart/Baden Wuerttemberg.) I DO have a valid ticket for December, as I wanted, and DO NOT have an ongoing Abo.
I paid for my husband's subscription directly with the same credit card but not via PayPal. I had to follow the cancel subscription link in his email to cancel the future months.
Both paths yielded the same result: valid ticket for December, cancelled for the future, but the PayPal method required fewer clicks FWIW.
Here is the exact text from the cancellation email for your reference:
"It was not possible for us to use the deposited charge payment method. That's why we had to cancel your DeutschlandTicket subscription.
The reason for this may be:
You paid for your first purchase of the DeutschlandTicket with ApplePay, GooglePay or PayPal.
In this case, it is not possible for us to make another debit using the payment method you have chosen.
We therefore ask you to use the credit card or SEPA direct debit payment method for your next DeutschlandTicket purchase." [Bolding mine]
In both cases, it was easy to purchase, easy to unsubscribe, and I presume it will be easy to use once we arrive in Stuttgart in a few weeks.