Severe slippage for 3 weeks

I personally experienced severe slippage between 10%-15% on my profit trades. It is so obvious when I close at that amount I see, but at history it’s less of at least 10%.
I have traded with ATFX for 6 months and never encountered such slippage until I made much profit that I noticed this irresponsible action was deliberately set on my account.
Multiple emails and video proofs sent to ATFX customer service but no action was taken. I have also highlighted to my account manager in KL but fail.