No stopping my debit order payments

I used the advertising services of Hotfrog.co.za. After a while i canceled my advertising subscription and received an acknowledgement stating " this is to confirm that you will no longer be charged for hotfrog services. However they have twice again debited my account and i had to use the services of my bank to recover those payments. I really dont care what there excuse is for unauthorized taking money out of my account but as far as i am concerned it was theft.