Yeah @goth.gaia gave an amazing answer 
Just ignore them, they end up disappearing and all us of had to face them at some point 
There are are a bunch of them, we just ignore them ^^
Also, I agree, they are ANNOYING.
Some bad stuff about Instagram:
It happens though, we have bots and people who are intent on getting lots of followers by following so many people, unfollowing, so their number increases or buying followers. Commenting stuff on your post even though they don’t care about you. Some of them advertise on your posts or send you a DM saying weird stuff, like click this link or inappropriate content or scams. Don’t click any link from these people ever or respond. Simply report and/or refuse their request. Luckily, these accounts end up getting terminated. Also, you have hate accounts pop up sometimes but they are silenced by getting reported. Thieves are also reported.
Instagram is awesome but like every social media out there, it has its “dark side”-quoting my friend Maria here. I would encourage you to have fun and enjoy it while not stressing over stuff.
After all, there’s something waiting for people who are bad on social media and off social media: karma 
Another tip:
Good luck with everything, shoot me a PM anytime if you need help 