True Results Got a collection notice after 1 year of paying off my account. Not received anything prior to this letter stating I still have a balance. Richardson Texas

I received a letter from True Results today it was dated Aug. 20 ,2015 I received in mail on 9/8/2015 it stated that my account balance is not resolved and to do the following : update billing info, establish new payment terms, or pay outstanding balance. Well the problem is I was finished paying this auto deduction over a year ago and before receiving this letter today I have not received anything stating I still had a balance owed or any statement. I tried contact the number they left and the end of their letter but it just rang and then hung up after it rang about 12 times. I tried calling it 3 times , they had no voice mail either or website to contact, nor did this letter state a balance owed and said it would be turned into collection company Quantum Collective Service if not heard from in 10 days . I did not receive this letter in 10 days. I would really like some answers and proof that I still owe anything because my contract I had was up last year and nothing was sent to me about it so I assumed it was finished. I had the surgery on 12-2012 and have paid any balances they have alerted me too. This letter is out of the blue and I don't want a negative report on credit . They sent to collections without giving me a bill or a chance to clear up any unpaid balances if any. I think they should of notified me atleast once in the past year if they weren't receiving my payments. I don't think I should owe anything. I have paid them thousands already as well as my insurance company. I hope someone can clear this misunderstanding up because clearing true results finance office doesn't . I also called their business office and got a voice mail with no call back.