refused to refund

i had an account with legit under EDCON which was inareas,i paid up the outsanding balance completely and they sent me a paid up letter too,two weeks back i mistakenly transfered money to EDCON amounting to R550,i called them asking for a refund and they asked me to send my documents and a motivation letter as to why i need a refund,i sent them all my documents and i also included the paid up letter they sent me just incase they need it,instead of a refund they emailed me saying they cant refund me because i owe them,i then told them that i paid everything and i have the paid up letter too,since then they haven't come back to me with feedback,please help i want my money back.