O2 flex you contract cancellation

I canceled this o2 flex  contract in December, and then I was told to confirm the cancellation , I 'd need to call, I called and I was told, the cancellation was  confirmed, the contract was supposed to end January 18. To my surprise , today I saw an awaiting debit from o2 in my bank statement. I decided to login, sadly, I found that the cancellation was shifted to February 17. This is cheating and very unfair.

The term with o2 flex contract is that you should cancel before the end of the previous month. I canceled in December.

I 'm demanding  this to be canceled immediately.   This is unfair 

Edit by o2_Katja: Verschoben Richtung Englisch