OK furniture store

I had an account for 24 months with OK furniture's where I purchased two cellphones and had to pay in installments over 24 months. In Novemner 2024 I went in store to pay my ccount because the debit order was returned, when I got in store to pay the cashier asked if I wanted to settle the account and I said no and I would pay the installment and then oay the last installment in December . According to my knowledge the last payment was supposed to be the following month December, but when I got there December the 1st I thought I was paying my last installment like the cashier told me the previous month, only to find that I now owed double the amount that the cashier said I owed the previous month. I then asked for the manager to explain how this could happen because I was told that im paying My last installment in December, he then printed my statement out for the past months that I've been paying my installment which is 23 months. When we went through the statement we realized that the payment I had made the previous month did not reflect on the statement , the manager then called rainbow finance (head office) where I spoke to the team leader and manager Esther , she explained that the payment had been picked up on her side on the system and that my new settlement amount after I had paid for Decembers installment was R417,50 . I them settled that R417,50 the very same day. She had sent the settlement letter and amount to the store , after settling the amount I got a receipt that said that I owed R0.00 my arrears were R0.00 and my account was closed ghis took place on the first of December. Fast forward to January 2025 I start getting calls from OK furniture's saying that I skipped my January payment and I owe them an amount of almost R1000 . I went back into the store to ask what was happening , they tried calling head office. When I spoke to the manager from OK head office (rainbow finance ) she was dismissive, did not want to listen to my side of the story and said I owe them and had to pay the money I owed. I have all my paperwork and proof that I have paid and the account was settled and I'm afraid that name would be tarnished , I'm being unfairly billed and I don't know how to settle this cause I'm not being heard by the management .