Payment done but according to them u still owe them

I paid my sccount last yr oct january i requested paid up letter till tiday they say i owe 800 my account is handed over to shapiro schaick i told the lady must send back the account to jet because i dont owe edcon a cent i magine full 6 months waiting jet and edcon its nonses thier excuse are dissaponting i belueve obbudsman can see