Owing Avon Account

I pay off my account , i was always following them every-time when i have done payment.sending emails to their credit control, my last balance its was R296.58. i went to pay it off in December 2018.on the 18/11/2019 they call saying i dint pay off their account ,they want prove of payment now.where i am gonna get the prove of payment. i called their credit department the guy told me i pad off, they refuse with the paid up letter.