It seems you have a good reasons to sue. You got perfect reviews. It shows your dedication to providing great customer service. Maybe you got carried away and said some things to the agent however the lockdown is unacceptable. She doesn't have the right to make these decisions. You should speak with senior management before to get your money out.
Suing probably won't help. The freelancer desperately needs money now. Suing requires you to spend money now in hopes of getting money down the road. Since Freelancer.com is based in Australia and the person they screwed probably isn't, suing would require sending spending a lot of money they don't have on an Australian lawyer, probably well more than the $3600 that's at stake. And if Freelancer.com is malicious or doesn't want to lose in public, they could drag this out a long time.
More than reason to, if they are holding money with no reason they would already received my Letter Before Action. It depends on what jurisdiction you are in of course
