There is no real solution here where you come off unscathed. You can either cave, and continue to give free work for the rest of eternity, or you can stand up for yourself.
If I have a problematic buyer that is clearly just taking advantage, I hold my ground and remind them that the order comes with x amount of revisions, after that they have to pay per revision. I normally just send an offer for the revision and then redeliver if they don't want to take it. Unfortunately, you can't protect yourself against buyers like these as Fiverr doesn't help much, you just have to brace for impact with the reviews and whatever effect their negative feedback will have on your profile. Reach out to CS again, and continue to redeliver if he keeps asking for unpaid revisions.
In the future, try to screen as much as you can. The more thorough and detailed your consult is and your requirements are, the more you cover yourself. Try not to ever work with a buyer that's obviously using Google translate, or have extremely bad communication off the bat. And, if my gut ever gives me a weird feeling, I've learned to trust and rather forego the work or cancel the order as soon as possible. I've learned through dealing with buyers like these that that's really all you can do