HLO Collection Services

I rec'vd a letter from HLO Colleciton Services. it is a typed letter stating that I owe a bill for Mid-County Dermatology. I have a record of all bills from 2018 until today of medical bills owed. I do not owe anything to this Dermatologist but $11.00 in which was paid because my insurance paid the rest. I tried calling to # on letter ***--i tried calling 3 times today 02/20/2020. at 10;51am--message came on stating that Kelly Zoff not avail. but VM was full so could not leave message. I tried again at 11:16am--same message. I tried again today at 3:28pm now getting message that says "we are unable to complete your call". the letter says to make a check or money order payable to our office, to include name and account # and send to a P.O. Box. I refuse to do this. When I googled this company there were 4 persons listed that lived all together in an address.