Client Services, Inc. Debt Collection Complaint

Client Services, Inc. Debt collection department,

Medical Cont'd attempts collect debt not owed Debt is not mine Florida

I a bill in - 2015 from - - - about the professional component '' of my emergency room visit to - - - for the amount of $620.00. I called my insurance company ( - - ) and they said that it is covered by their - - and that I should not have received a bill. They sent - a Balance Bill Letter. Later, on - - ( Dated - - 2015 ), I received a courtesy notification from Client Services Incorporated for the same bill that it will be going to collections in 30 days if I do not dispute it. I want to dispute it, but I do not know where to send the letter since there are - addresses on the bill and do not specify where to send the letter of dispute. I am afraid to call them again because when I did they were very abrupt and kept changing the subject and asked me for my personal information like what is my previous address. They also said that it will go to collections on - - since they received it on - -. How do I keep this off of my credit report? I am willing to pay it if I know I will be reimbursed later but it is unclear if it 's - - 's or - 's responsibility.