Jet is horrible

My jet account was paid in full in 2020/09/10. After that I have not bought anything from them again. Longer than a year later I receive an sms that I owe Jet R336.00. SMS dated 09/12/2021. I have emailed them numerous times with the statement that was paid in full and asking for statements or accounts as to what this R336 amount is. They have yet to give me any feedback until today the 21/06/2022. Now I have been handed over to debt collection MBD. I have not signed up for any clubs or funeral plans etc. Their service is pathetic when it comes to customer service. Many years ago they charged vodacom airtime on my jet account and I did not even own a vodacom phone then. How am I supposed to get feedback from these people