Debt Collection Call a year later for account that was closed and paid up in full

I have been contacted by a legal department stating that I owe Fedhealth R400+ rand. Firstly, at no stage in the past year have I been informed of any balance? I closed my account with Fedhealth and made full payment, so I do not appreciate the way that this has been handled by your team. Please send me statement asap and how your team has come up with this balance, you are effecting peoples credit record here, its not a game. When I needed a doctor, your team was not able to assist me, they didnt know who my doctor was suppose to be and ended up giving me a random address with no visible medical center to be found, I had to end up paying for a private doctor, I received nothing from Fedhealth in regards to service, hence cancelling which you should have on record as well as all the payments I made.