Go to your account settings, there you will see "notifications" click there, and just click or unclick what you want to be notified for! :)
Click on your profile icon at the top right, click on the account settings section below. Click on the "notifications" tab and uncheck those you don't want to be sent.
I suppose to mean that your notifications number won't go down. It is just a glitch, and you aren't the first to ask this question. Nor are you alone with the glitch.