Double Billing

i have been billed double on my january instalment. i have been to the branch only to be told that the 2nd payment does not appear but they see it on my statement, and i must wait 3days. i called the call centre and still 2nd payment does not appear. now what do i have to do to get my refund back as i know for a fact that when the debit does not go through i get numerous calls t arrange for payment and when you are the ones owing me i have to struggle. tell me what do i do with my other accounts?