Why did I not receive my PVP reward for reaching a new league?

PVP rewards are sent at the end of the tournament.

You may have reached a certain league but it doesn't mean you will stay in it until the end.

You therefore need to keep on fighting to keep the level you have or to level up again.

Then, at the end of the Global tournament (PVP), you will get the reward corresponding to the league you are in.