Are there any experts who can answer questions about the redemption of the 513050 ETF fund?

I bought 1 million units of the 513050 ETF from E Fund on February 26 within the market. Then I submitted a redemption request on the same day. Initially, I was charged a redemption fee of 5,000. According to the net asset value (NAV) announced by the fund company, the NAV on February 26 was 1.3069. My understanding was that the amount should be 1,306,900 because the fee was deducted separately from the cash in my securities account, which had already been collected. However, after T+4, on March 4, the actual settlement funds credited to my account were only 1,290,329.98. Where did the 16,570 go? I asked E Fund customer service, and they explained that ETF redemptions involve a netting process and the actual sale price does not necessarily equal the NAV, and it is not publicly disclosed. The amount settled is just what the securities company provides. This is so opaque. Even if I didn’t sell on February 26, the Hong Kong stock index still rose on February 27, so why is there a shortfall of 16,570?
In the end, the answer is: they give you whatever amount they settle, and the settlement price is not disclosed and cannot be checked elsewhere. Who can I hold accountable for this?