Wesbank does not want to refund me

With the FNB online banking I mistakenly transferred R49000 to the Wesbank account. I asked for the refund from Wesbank (which took time to be partially refunded). I received the refund but it was not the R49000 I transferred. But, instead I received R46361.94. Then, I wrote back to them to know what happened to the R2638.06 they took from the R49000 without any explanations. But it has been a month and still no response. So I thought they deducted it for the next month car installment, surprisingly the next month car installment was deducted (from my bank account) in full. So I have not received the full refund as yet and I still do not have the explanation as well. This is not fair, it's bad to take anyone's money without an explanation. So my money is ******? where is my money?