Medical aid ******ion

Hi. I have cancelled my membership effective of 31st August and I have a certificate for that, of which I still had money in my medical savings account but I'm now sent something saying I owe discovery R1052 or something like that that was claimed on the 14 September 2018 from my account as clawback, how is that possible? I only used discovery for 2 months and didn't even exceed my medical savings account money but paid more and now I have to pay you, so I'm confused and angry. If only I knew you ****** people like this I wouldn't have chosen to work with you