What du you mean by “ automatical monthly deduction” exactly?
Do you want to stop the automatic renewal of your package?
Enter Mein o2 an visit the following page: https://www.o2online.de/ecare-prepaid/tarifdetails
Find your active package an than press “Abbestellen” to cancel the package.
On the next page you will be asked, if you want to cancel your package immediately ("Sofort abbestellen") or at the end of term ("Zum Laufzeitende abbestellen”)
Do you want to stop the automatic top up your credit via your bank account?
Enter Mein o2 and visit the following page: https://www.o2online.de/ecare-prepaid/automatische-aufladung
Uncheck the marks and than click “Speichern" (save)