Unauthorised debit order

I was debited with an amount of R300.00 on my account. I did not accept their package at all. The moment i saw they want you to pay for a loan i stopped with immediate effect and exited. Now this ***** of a company passed a debit order. Who signed for this i would like to know. I want to sue for damages as that was the last money in my account and i have no petrol money.