unknown number able to see me online

It is problematic if any unknown person having my number can access my profile, not only this but also can spy on me when i am coming on-line , and when last seen that too without my knowledge, that they have my number and are spying. Its very problematic. I want whatsapp to have some solution to atleast stop them from seeing me online or offline, before we have any conversation on whatsapp, so that i can block them thereafter as now me too have there number.