Uathorised debit order

my account has been debited by South African payment exchange. I have never been contacted by this company. I want to know how they got my bank account as I don't know anything about this company and they must cancel this debit order as I do not have any business or contract with them. I tried calling them on this o ********** the number I was given by my bank when I realised that my account has been debited and no one answered the whole day and this makes them look as a company with no customer care as they never responded to my query I sent via online