HANDED OVER TO DEBTOR COLLECTORS

I visited lancet in umhlanga in July 2014 for a blood test. exactly after 1 year I receive a call from Bongani from SUSTAINABLE COLLECTION SERVICES stating I have been handed over to a debt collector for an amount that I owe lancet. according to my knowledge my medical Aid sorted out all cost as I didnt receive any invoice from Lancet and on my medical aid statement it showed lancet was paid. why should I pay for something that I didnt receive an invoice for ? secondly the debt collector has been stalking me for the past two weeks and on our first call on the 15/06/2015 I did advise him to send me a statement. its been over a week I only received the statement today the 29/06/2015 and on that invoice I am also being billed for calls that the debt collector made to me R19.38 PER CALL X 4. LANCET WAS *********** NOT TO SEND ME AN INVOICE AND TO HAND ME OVER TO A DEBT COLLECTOR.