Unauthorised debit

Today 22 Sep 2017, when I checked on my bank statement, I saw that there is an unauthorised debit order of R 359.00. I do not have any loan contracts with this people and it was my first time finding out that there is such a company. They are a ***** because I did not give any consent to debit any money from my account. When I try to contact them, the phone just rings for a long time.