********** activity approved on account

I had another debit order go off my account today, 28/12/2021. When I made an equiry I was told that it was a prepaid Sim converted into a contract. I do not even know the nr and when I contacted it someone unknown to me picked up. Firstly how did they even authorize this without confirming details with the account holder who is me first. I have to answer all these security questions in order to obtain information so how was this new contract done? I need this to be resolved as this was never authorized by me