Lack of allocating payments

In April I saw on my statement Edgars did not allocate my payment made 31 March, I send prove 14 April and I checked with my bank that payment did go through. I received reply from Edgars that day that they received my prove but it is not allocated yet. Nothing again. My May statement clearly showed where the 31 March payment has been allocated. My account was paid every month and I was in advance 1 July, according to my calculations with +/-R50. I bought items on the 8th and wanted to return them on the 9th. So they made me pay an amount before I could return, after the payment they still told me I cant return. I immediately drove to another branch where exactly the same happened. They called customer service and that lady told me I did not pay my installment. Today my July statement arrive and the payment made 1 July that was supposed to put me in advance does not reflect. So my payment was not allocated twice in 4 months and they treat me like a ********. I am disgusted