Actually a chill is just the DTCC's Refusal to clear transactions everyone is allowed to trade and short. The Blocked Trading is because the Brokers refuse to use another clearing house or hold your transactions untill the DTCC lifts the chill.
The only Agency that can freeze a stock or security is the SEC.
It hasn't blocked my Zecco account, but my ameriturd accounts are blocked. It appears with 99999999% shares today that traded were shorted that means nite has an endless supply of no shares! , oh I mean shares! LOL Apparently at their hedge fund or whatever all you need to know is Sell sell sell and then sell some more! Dont' check to see if there are any available shares to sell just SELLLLLLLL!!!! Anyway that's the way it seems. Just my opinion . Tough to beat the house when they have all aces and face cards in their deck!