Double Payment not being refu

I made use of EFTPOS services in my shop it was cancelled at the end of June 15 at end of July the informed me that there were still an outstanding amount on my account I paid this the end of July via EFT, just to find out that they put through a debit order at the beginning of August for the same amount, my account number :AR/*** - I have been trying on numerous occasion via e-mail to ask them to refund the amount, they don't even have the decency to respond to my mails! The salesman in charge Novin has ask via mail to sort it out but still no joy! Be careful to deal with them!