To cancel plan by mistake after subscribing and cancel my debit with credit card

Hi. I'm not good at German. It's hard for me to understand the system of  O2.

I want to cancel payment of data pack S by mistake. I didn't use data of this data pack.

And I set up charge debit card payment for insufficient credits. I didn't have enough money when I bought My prepaid S. So I have debit in my balance of Mein O2.

Could someone tell me how can I cancel the plan of data pack, and payment by credit card? Thank you!