Newton's second law of motion states this (verify on Wikipedia): $$\vec F_{net} = m\vec a$$ Here, $\vec F_{net}$ is zero, so $\vec a$ is zero too. Going back in reverse (what you did in question), $\vec a = \frac{\vec F_{net}}{\vec a}$ can only deduce that the body is experiencing no net force. That's it.

Feel free to use Law of Gravitation, Coulumb's Law etc when the force in question isn't the sole cause of the effect. Newton's second law of motion can't help here.

Newton's second law of motion states this (verify on Wikipedia): $$\vec F_{net} = m\vec a$$ Here, $\vec F_{net}$ is zero, so $\vec a$ is zero too. Going back in reverse (what you did in question), $\vec a = \frac{\vec F_{net}}{m}$ can only deduce that the body is experiencing no net force. That's it.

Feel free to use Law of Gravitation, Coulumb's Law etc when the force in question isn't the sole cause of the effect. Newton's second law of motion can't help here.