suspiciously very high commission

I input the amount of 46000 which is about $311 to BUY in AUDJPY. in just a mere second, it auto closed and got a negative value of -2738.88. Upon checking, the commission is way too high for about $-3047. The v5 app is just auto responding saying that the commission is set by TradingWeb Exchange and they can't intervene. They are also repeatedly saying that commission are updated every week. I was asking where can I get claims for this due to the app error or bug but no reply.