5 yrs ago i was under the care of a chiropractor. he recommended a procedure under anesthsia . i told him i didn't want to do anything not covered by my insurance. i had the procedure, and paid the bills i was sent. yesterday i recieved a bill from a collections agency for $1,966.12. on the bill there are several entries as non covered write off. i never heard from them or recieved any bills. this was 5yrs ago am i legally responsible for this? will this be on my credit report?