[jahewson]

Does Upwork have a binding arbitration clause? I’d expect them to.

In which case, take them to arbitration! It’s pretty easy for you but costs them money.

[Animats]

Yes, their terms say they use JAMS under California law, which is not totally unreasonable. Read their terms. There's a dispute resolution procedure. First, they get to sit on your claim for 60 days, and then you get to go to arbitration.