I have always paid my bills on time. About 15 years ago I was harassed by a third-party debt collector over a Bell South phone bill that was not for my phone number and I did not owe. Bell South had simply sold this unpaid bill (which was already a eight years old) to the collector and attached my identity to it. This debt collector called constantly at home, at work and harassed me in every way possible - including threatening to send cops over to arrest me. It also showed up on my credit reports and my credit rating dropped drastically.
Bell South (or their legal department) would not help me. The State Utilities Commission was of little help (except to give me the number of Bell South's legal department). I eventually had to hire a lawyer (for several thousand dollars) to resolve the situation. The clowns involved would not fix my credit report, stop harassing me, or unlink the phone bill from my name until I had a lawyer send letters threatening to sue them.
This was over a phone bill that was only $230 in size that was for a phone number not associated with me. Eventually Bell South had to settle with the state regulators (five years after this happened to me) stating that they sent many people to collection who did not owe bills due to "bad data uploads from Bell South to the debt collection firms".
Keep in mind what the credit industry could do to people who do not owe bills and can not afford a lawyer. Especially when the debt collectors can now use the criminal justice system and cops to drag you into prison based on dubious evidence that you even owe the debt.
Keep in mind that debt is a civil transaction -- any disputes should be handled strictly in the civil court system.