[NickHirras]

Section 6.5 discusses non-payment by client, and charge backs.

https://www.upwork.com/legal#clientpayments

I think just to preserve brands goodwill, Upwork should absorb the cost (which they have to this point), pursue legal action against the client, and not punish the freelancer.

I don't know the legality of withholding payments for future work due to the freelancer. I don't believe they have a right under the terms to do that, but I would not do any future work for free. That could be a breach of contract on Upwork's part, although haven't read through these terms enough to know that.