Go here https://www.bbb.org/en/us and start the process

When they ask you which company, choose Bittrex Inc, Bellevue WA

They'll direct you to the Northwest version of BBB, follow the process and when they ask you if there are crimes or any serious legal thing involved say NO. Say no to everything that would normally require a real lawyer.

Anyway I don't know for how much this system will be useful, when I used it they had already received 222 complaints in few days, now they're at 500. They're being rapidly flooded so they might soon stop helping people as well.