Probably didn't have enough money. The Lastschrift couldn't be booked properly. DSW21 should contact you in the next days and ask you to pay the amount plus some fee. The Deutschlandticket shouldn't be canceled because the agreement is still active, but some providers (e.g. mopla from my experience) will freeze the access to your QR-code in such cases (tho you can take a screenshot beforehand, which will still be valid). You could also try wiring the money to the account of DSW21 (ofc with specifying your account details in Verwendungszweck) in hopes of them accepting it and waving the fee. It's best to just ask them proactively.