Anti-Cheat? They accepted my screenshots of 500 prestige for the first quest (at 300) and the second quest (at 400). The problem i'm having is the third quest (600 prestige), since moving forward with the game actually skips you from 500 to 750 if you remove all your prestige boosting equipment.
lvl 10 is hard It's not particularly hard, you get plenty of xp from pvp games; with GGs it's around 500 per loss and 1000-1300 per victory and you only need around 6000 per level. I've just been playing enough to gain 1 level per day and I'll still have an extra day left after hitting 10.
Another Nickname The only advice I can give is to message Gamekit support/put in a ticket about it and hope they let you change it.