I owed XXXX dollars to my previous dentist. 
They sent it to a collection agency with wrong contact information, wrong phone number and wrong address. 
afterwards as I was applying for home mortgage, the bank figured it out and gave me the collection agency phone number. 
I paid the balance in full the same day. 
After that I asked the collection agency to remove it from the credit reporting they hung up the phone on me. This is the only incident that negatively affected my credit history all my life.