I know that, but the relativity of simultaneity is for causally unrelated events while these events are causally related.
Right, but FTL breaks this. Did you read the rest of the page? It described in detail a scenario in which the response to an FTL signal would arrive before you sent the original signal. This being in your own frame of reference.
FTL is time travel. If I'm not explaining it in a way that you understand or that seems convincing, just google it. You will find no compelling arguments to the contrary because, assuming special relativity is accurate, there's just no way out.
But the new ideas about physics are as unproven as the old, so regardless of where we place the burden of proof we shouldn't automatically assume one is right and one is wrong.
Of course we can't be wholly confident of anything. But it takes nothing more than some logical thought to understand that time can't be a literal axis. And even if it were, suppose you traveled backwards in time to Earth of 1915. You arrive one hundred years ago, and then what? You won't find Earth. Earth isn't located in 1915 anymore, it's located in 2015. The entire idea of meaningful time travel is preposterous. It's riddled with paradoxes and impossibilities.
Granted, since FTL and genuine time travel are both violations of causality, we could just say that their existence depends, for one, on the integrity of our understanding of causality. Break causality and you're one step closer to FTL and time travel, though since events can no longer be reliably said to be ordered from cause to effect I think that you would have bigger problems.
NASA says it depends on two things: spacetime expanding faster than light, and negative energy existing, both of which are considered likely.
From that link: "First, to create this effect, you’ll need a ring of negative energy wrapped around the ship, and lots of it too. It is still debated in physics whether negative energy can exist.", "Regarding the physics of negative mass, it is not known whether negative mass exists or if it is even theoretically allowed."
http://physics.stackexchange.com/questions/44934/does-matter-with-negative-mass-exist
Also from that link, "And fourth, if all the previous issues weren’t tough enough, these concepts evoke the same time-travel paradoxes as the wormhole concepts." Though they don't seem to discuss the physics of it.