Instagram following strangers?

So on my Instagram i got about 400 followers and i only follow 2 accounts. Every 2 weeks though when i check how many people i follow it says i follow 3 or 4 and when i check them they are total strangers I've never followed or interacted with in that or any platform for that matter. I did Google this, ive never used a 3d party app but just in case, disabled the option from the settings and changed my pwd as suggested by most users but as far as i can see thats for ppl that have used some kind of follower booster etc. It keeps happening no matter what i try and it's annoying. can someone plz explain to me why it's happening and if there is a way to stop it?

Thanks.