Is this legal, what should I do?

After finding out that I got declined for a business credit card, I decided to find out why that was the case by reviewing my credit report, then to my surprise I found out that I have a collections statement on my credit report.

I called the debt collectors office and they said they sent out 14 letters notifying me that I owe a bill from my dental office, however the address they sent those to is my father's address, I don't live with him and I have never lived with him so why are they sending it there? My father has not even contacted me to tell me I owe a bill or they are trying to contact me. The dental office has my address and phone number so why didnt they contact me and why didnt the debt collector contact me before putting a collection statement on my credit report is that legal?

I did move however I still had my old cell number up until last year and I had all my mail from my old address forwarded to my new address so what happened? The collections attorney said they are filing a lawsuit in a couple of days if I dont get paid, but I told him well how can I pay and how can this end up on my report if I never recieved a bill or any notification. I spoke to my father and he said he made a payment to them and he agreed that he will pay monthly until the bill is paid up but he stopped apparently. I have to wait until thurs. to speak to the a woman in charge of billing who won't be in the dental office until thursday.

Is this my fault and should this be on my credit report if they made an agreement with my father and notified him, instead of notifying me as the patient??

I paid my balance which was over a thousand dollars the day of my services and the rest was billed to my insurance. I was billed again by the office for a payment my insurance did not cover at my old address and I paid that!