Took two payments without authorization

I have a loan with these guys and this month for some reason they debited my account twice in 2 days. Both payments were full payments of R1250. When phoning to sort this out i cant get through to anyone. I have tried 16 times in total and spent R40 in airtime to get a hold of them but no one answers the phones. Tomorrow i will go to the bank and reverse the payment as there was no authority to do this. I need answers because the money they took was half of my rent so i cant pay my rent because of them!