Bank charges

Hi, I have noticed a charge on my account which I have not authorised nor have I agree to this when opening my account. This was not explained to me, and how is the bank able to take money from a client without notice or explanation before doing so. I am being penalised yet I did not consent to this. My card should have declined on attempt to purchase if there was no funds. I would like this matter resolved immediately as you are robbing me of my money.