Hello!
Obviously, I'm just writing not to bid (...) but to have more info and to help, if I can.
For me: could you please let me know the name/user ID of this cheating employer? I wouldn't deal with that topic :-), but he could have something different to make translate.
For you: 1) have you already tried to ask freelancer.com support t do something - to ban him or so? I suppose you could show your good will and his bad and they could (hopefully) check your private corresepondence?
Then, 2) there's at least another translators' platform that - at least some years go - used to prepare, update and sell a list of bad employers (non-paying, delaying, cheating in multiple ways); if you are interested, please let me know and I will try to find what site it was.
Then again, 3) I've painfully/angrily had myself the same experience on another platform but, luckily, there it's possibile to expose the cheaters, release in any case a negative feedback and - happily again - I had the opportunity to threat him (I had his personal email) to send him some debt collectors :-). This way, I finally was paid, in a blink of an eye.
I suppose it won't be your case but 4) is it really likely to be impossible to tell directly his clients that since you haven't been paid, YOU own the rights for that translation and could sue them if they use your translation? Maybe I will sound naive :-) for this case, but sometimes it seems to have worked.
If needed, please contact me. Good luck! workisall