PvP Questions

Hi, people.

I have some questions about the types of pvp in the game. I found no related topics at a first look.

For some reason I'm never able to join to 20 vs. 20 and 18 vs. 18 pvp. I always leave them marked on the dungeons screen and nothing ever happens. When I go to the npc that holds the battles (or so I presume it is, I just click in the blue chinese name that shows there), get no better luck at all. What could it be?

On the 1 vs 1 pvp, that happens every saturdays and sundays, that I always believed that was Galaxy Arena (it isn't?), I can't get a single athena tear, no matter my position in the ranking. I got 4th place at bronze category with rank 3 last week, I'm currently in 4xth place at silver category with rank 6, the only prizes I get are cosmo runes, blood, enchant pot etc. Wasn't I supposed to get some pvp flags at the end of the battles as well? I get no notification or whatsoever after it.

Please guys, help me, I wanna get my first gold cloth haha.

*I'm level 75 and 70k power, if it's somewhat relevant.

For galaxy arena you got your reward at the end of the week but if you want a good reward you have to play every single day there is galaxy arena.
And for the pvp war i don't know which time do you play ?