Why my plugins are updating automatically?

That might be a problem coming from your settings when you created your WordPress website.

Are you using a cPanel and an application that automatically takes care of the WordPress installation for you?

For example, I use ‘Quickinstall’ (you might be using the same application, or Fantastico or something in that sense).
There’s an option in the settings:
Enable Global Automatic Upgrades:
– Unchecking this will disable Automatic Upgrades for the entire account.

My guess is that you have this activated, so as soon as it finds an update it does all the work automatically.