My game slow down after some secondes

When i try my game in phone, after some seconds my game slow down, each second it gets slower
my game simple:
the Player run ((not moving) and Jump ,the Enemies move from Right to left, After Enemie leaving the screen and is n collision with an Off-screen object (Wall) , the Enemie deleted
but i think the Enmie not deleted and I think it is the reason my game slowed down
If this is the reason, how do I delete objects without slowing down the game?
A picture of delete Enemies:

َA picture of the enemy movement:

In general peoples have this issue because an action is called at each frame and is accumulate.

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