Disappointed Customer

I have by accident made two payments to game on the second of July for our account. Then after that I have decided then I wont be making any payment in August because of the double payment in July. My account payment was R582, I have paid R582 and the a second payment of R888. Now game is constantly phoning me everyday saying that we owe them R495 for July payment. We have phoned them, trying to explain but they refuse to listen and says that we are a payment behind. If you have a look at our June statement it states total due R582, and nothing in arrears. We paid the R582 and made a second payment of R884 by mistake. Why cant the R884 then not be used for for the R495 payment on the July statement? I have just paid the R495 now, because of you guys phoning me numerously. I then expect for you to please refund the R884 back into my account, because you are unable to allocate that EXTRA payment to the R495.