When you press either the Facebook, Instagram or Phone Number login button on the app, we set up the profile using the content from either your Facebook, Phone Number or Instagram account. 

It sounds like you may have hit multiple of these options at one point but continued to just use one sign-in method as your main account. To delete the other one(s) you just need to sign in with the method you do not typically use, then head to: 

(iOS) My Profile - Settings - Support - Close Account

(Android) "..." in the top, right hand corner > Support > Close Account 

This will allow you to delete the duplicate. I hope this helps and let me know if I can assist with anything else.