Best and home electric is ******** customers

Good morning I've got a serious problem with best home and electric on January I've paid my account at store cause usually I'm using EFT to pay ok so on that January I've paid total amount of R531.14 and the outstanding balance says R3561,62 that left okay Friday I've received the statement that state how much must I pay this must and how much is the outstanding balance surprisingly the amount increases and last month again I've made payment of R531 but the amount instead of decreasing it increase so on that outstanding I've saw on January after payment R3561, 62 I've made payment on February but the statement of March says I'm owing R3851.31 so I fail to understand and that state this thing has been happening for such a long time but I was not noticing it