I have two sizeable ones on my history that I cannot get removed. One is a medical bill from a facility I have never even seen (about 60 miles from where I used to live) and the other is from a utility company with whom I have never had an account.
It costs you nothing to put those accounts into dispute. It's up to them to prove you had an account and did not pay. They won't likely fess up right away but if you press they'll have to fix it.
