You still haven't answered the question. Why did you lie about the fact that you received 16 BTC from said user:
We haven't received those 16 bitcoins.
If you didn't receive those 16 bitcoins why are you refunding him now without any objections? Or, more likely, why were you previously denying the fact that you received money from the user, when clearly it can be seen on the letter of guarantee that he has deposited it? Also, why did you make comments about how the letter of guarantee could be easily manipulated at the start of this accuastion instead of trying to address the situation sooner?
the latter of guarantee easily can be manipulated
Anyways, don't think that everyone's on you just because of Chipmixer. It's because you are a shady business.