When you block someone on Instagram they will not be notified.
Tap (iPhone) or (Android) and then tap Restrict [username] or Unrestrict [username]. Restricting someone’s ability to comment will also affect direct messages. If you have a public profile, they are still able to search for your profile. Any attempt to send a direct message will move to a message request, according to Instagram, and notifications … With Instagram’s Restrict feature, though, it’s sort of the opposite: When you Restrict someone, only you and that person will see the comments they’ve left on your posts… You can choose to stay or leave the group. Restrict or unrestrict someone through a comment. Swipe left over the comment (iPhone) or tap and hold the comment (Android). Neither you nor any other person will be able to see it. Instagram users can now "restrict" any chosen individual, which gives a few, immediate perks. However, they will no longer be able to see your content or message you.
What happens when I block someone on Instagram? To restrict or unrestrict someone through a comment on your post: Go to your post and tap View all comments. The comment made by the person whom you have restricted will only be visible to them.