Isabella Garcia debiting my account without my approval

I have been receiving calls from Isabella Garcia convincing me to purchase their skin products and I finally agreed. I did emphasize that I didn't not want any contract with them, but I would be happy to do a once off purchase and that is what we agreed upon. The next thing I see a debit order with a contract number that I can't even reverse. I did not sign any contract, when I try to raise it with them, I am not getting response, and I would like them to cancel this thing as I mentioned I don't want contract. To my surprise apparently that is what they do to people. I regret even talking to that agent on the phone.