Some notes:
In order to work with OnCollisionEnter:
At least one object should have a non-kinematic Rigidbody and the IsTrigger option of the Collider should be not checked. Both objects should have Colliders attached.
To work with OnTriggerEnter
At least one object should have a Rigidbody and both should have Colliders with IsTrigger option attached.
These options are probably same for the OnCollisionEnter2d and OnTriggerEnter2d.
You should use Collider2d and Rigidbody2D instead
Good luck : )
