Onair have me in arrears yet I have paid my account in full!

I would like to voice my dissatisfaction with this company..they have my name in arrears an yet I've paid my account in full...they are not giving me no assistance...they whatsapp helpline is useless also nothing comes of it..sometimes they would bill you twice an when u reverse the one payment they have marked as unpaid.. I went through hell...can they please clear my name from there records as I've paid all my installments in full! When I apply for any cards they have me arrears! I will take up another contract with onair! Very unhappy client