Do you have any evidence to back your claim? If you had taken screenshots it would have helped but as icopress stated, a Letter of Guarantee would have been the perfect evidence. Do you have it?
A letter of guarantee would reveal sensitive information that they might not be comfortable sharing publicly. If that is the case then I would advise to share it through anonymous communication with a trusted member, like icopress, who can then confirm if they were scammed. The OP has not returned to the forum since making this accusation so it might remain unsolved.
That user claims they received a reply from YoMix on Telegram but I can’t find any Telegram links on YoMix’s website or announcement threads. I wonder if this user is trying to scam people by pretending to be their support.
I did find this other
accusation on Reddit, translated from Russian:
"There's nothing good about this mixer, it left me, it's been 16 days, and nothing came. Technical support is silent. Avoid this [banned mixer] scammer. If someone is interested in screenshots and the like, Telegram also has scammers for this support."