Not until the final invoice has been paid. This is the single most common way people end up in German debt collection after they have already flown home.
The closing bill usually arrives four to eight weeks after the contract ends. If the account is gone, the direct debit bounces.
German providers pass unpaid bills to collection agencies quickly, and the first you hear about it is often years later when you apply for credit back home.
Keep the account and the direct debit mandate alive until the closing bill has cleared.
Only then cancel the mandate and close the account, in that order.
Not until the final invoice has been paid. This is the single most common way people end up in German debt collection after they have already flown home.