Threatened by Collections Department

My one account had a mistake on it therefore the Medical Aid did not pay it. I was sent various mails from Netcare Union Hospital of which I forwarded to the Medical aid to pay. I had no feedback ever from the Union and after a year they handed me over to their Collections Department. My complaint is that when the Lady from Collections called me, she basically threatened me that I would have to pay the large amount apparently outstanding within 6 payments. They should be more helpful in helping clients to sort out their problems and check their processes.