Hi @Chachi,
welcome to our community 
So that this does not happen, we write on the invoice whether it will be debited or whether the amount is to be transferred
If it is a contract, the transferred amount will be automatically charged with your next bill.
If you want a refund to your bank account, there are 2 ways:

1. You can have the direct debit reversed, but this will cost you a charge of 4 EUR (I do NOT recommend this procedure).
2. Or you contact our colleagues on the hotline and arrange a payout of the credit. This takes up to 14 days until it is visible on your bank account.
   For this, it is necessary that your transfer has already been posted to your customer account. Therefore, the question: Did you specify your customer number in the reason for transfer?

Kind regards
Larissa

Yes my Customer Nummer was specifie..How could i contact your hotline or do you have Email ?

Hello @Chachi,

you can find all contact ways to our support here Kontakt aufnehmen und Hilfe finden | o2 (o2online.de) We also offer support for English speaking customers. 

Best regards

Giulia

Ok thanks..,