Follower notifications not working.

I can understand how this may be annoying, but if you block them you shouldn't be able to receive any notifications or messages from them. Whatever you do you should avoid replying to them because then you are creating an opportunity for them to be able
to report you which could possibly end in a suspension if the enforcement team deems a violation. My best suggestion would be to edit your privacy settings to either block or friends only so that you can avoid future problems, and if you do run into issues,
block those individuals so that they are shut out and report them if they have violated the Code of Conduct in any way. If you have your privacy setting for online status set to block or friends only then you wouldn't need to put yourself on DND or offline.
Unfortunately there are those that only want to torment others but if you use the right tools, you can make your gaming experience more enjoyable. Best of luck to you and I appreciate you coming to the forums so that others can learn from your experiences.

1. Press the Xbox button
    on your controller to open the guide.
2. Go to Profile & system, then
   Settings.
3. Select Account, then Privacy & online safety

I did report them but I haven't blocked them yet.

I did, but I haven't blocked them

Have you reported and blocked them?

if they message you click on the More button under the message and report it.

if they keep spamming you with notifications go to their profile and report them.

in the details box you can add that they are harassing you by spamming you with notifications