Axitrader - Limit order filled at worse price

Hi all,

now I noticed that my limit order was triggered in worser price at XAUUSD. Like I know its impossible to get worser fill in limit requests. This broker is regulated if its okay by the law and that I wonder? I contacted with the broker and they told me they perform slippage on both negative and positive ways on stop and limit orders. I worked in this sector before and in it is not possible to find worser on limit orders. Do you men think it works if I create a complaint to FCA?