are you talking about the coin glitch?

The reason that you get banned is because you're not adding any value and you're simply just being toxic.

Everyone starts with 2400 food now, and when the round restarts, 3000 bonus is given. If coin was 5000, and someone joined the game during game-over stage, then he/she will start with 5400 food next round, and can buy coin right away when the round starts. If anyone can buy coin that easy, then coin will lose its value.

Plenty of coins are being earned at 15000. It's not that hard :)

can you be more specific about what kind of rank you're talking about? are you talking about global ranking?