TIPS FOR EVERYONE:
1ST - The damage of the ball is calculated by the speed of the ball, so when more faster it is the ball, more damage he will give. Try aim by different positions to see the damage
2ND-The game have a lot of different enemies, but to reach them you need to increase in the waves. For example on the wave 14 you found about 3 different kind of enemies.
3RD- Focus on destroy the robots after you destroy the spawners. If you do this, you'll be better and 'll be more easy to reach far.
4TH- Start attacking the enemies top and after that go below.
These tips are only to let the game more easier to you. If you are playing by a different way and reaching far, that's very good. Keep doing this that you'll find a different enemies.
Comment below who reach on this crazy one ...