Money disappeared

I placed an order at Homechoice,for some reason in my account a positive balance of about 600 Rands was left on my account. The lady I spoke to said the money can be refunded back to me or I can use it to shop in future. Two months ago I placed an order of an Item worth 805.00 hoping I can utilize the positive balance on my account and then pay the difference. To my surprise at Homechoice they are charging me the full amount and if I ask about the money already paid I don't get a clear answer, only they are harassing me per phone calls and SMS s asking for their full amount. I wrote emails asking about the 600 Rands but I have received no answer. One lady who called asking me to pay I asked her about the 600 rands but she denied the money and when I asked her where the money disappeared to she said she does not know. I can not pay Homechoice a full price while they are holding my money hostage. I want the money used and I can pay the difference. It is my money after all. How can money just disappear and they contiously harassing me for more money.

Thank you K. P. Cele