Discovery Bank so unhelpful and unsafe

I have held a Discovery card for many years, and while it was connected with FNB I had no issues. Since moving across to Discovery Bank I have had endless issues and so many attempts at ********** transactions. This does not happen with Standard Bank, as they will call if any ********** looking transactions. Recently I had a large ********** amount processed of $1058. This amount was disputed and I received a refund. However, due to the exchange rate there was a shortfall of R1563, which I was charged and which Discovery gained. When I disputed this I was told sorry but nothing can be done, so I am out of pocket for R1563:(