Double billing my account

Discovery is currently billing me for two medical aid accounts. Discovery are aware that my one medical aid account has ended, as they were the ones that ended the account and issued me with a new membership number for the other medical aid. Yet they continue to take money off my account, essentially double charging me. Discovery's current business practice is dishonest and quite frankly financially burdening my family and I. Their blatant disregard for procedure and due process is an abomination.