The Six Flags shares that you have (or had), are under the symbol SIXFQ, and they are still in the bankruptcy process. They will most likely be wiped out, it just hasn't happened yet.
Announcing bankruptcy doesn't wipe out the shares, typically it will take at least 6 months until everything is worked out, at which point you can still trade the bankrupt shares. But unless there are assets left over, you'll get zero for them.