FINAL UPDATE: I cancelled the order, and took $70 loss, and Customer Support finally responded to my request of adjusting my completion rate, with a semi automated reply which felt like they didn't even read my message and just said "We can't adjust the rate due to buyer not being satisfied". I responded again, explained everything again, with screenshots proving that we agreed beforehand what was included and what was not included, and the buyer asked for exactly the things we had decided were not included, completely out of scope and impossible stuff. But they still didn't accept my request to adjust completion rate.
At this point, it is what it is, there is nothing I can do, and this just shows that the buyer can cancel any order for asking for revisions which are completely unrelated to the gig offer, out of scope and impossible to do, and Fiverr will support them and cancel and not even adjust your completion rate. Worst experience...