Misconduct of Treating clients fairly

I had to pay R4805,69 on the 7/11/2024 including interest as I had borrowed R4000 against my phone at cash crusaders three rivers branch.

I made a payment of R810 in the morning 07/11/2024, I later went to pay difference today of R3990,67 that is due today as per agreement however the manager Johny says I need to Pay R4589.95 as the R810 I paid earlier doesn't count as it's a new contract which i fail to understand. I have paid the amount as per agreement. I paid the amount he wanted but I am not happy with his outcome and promise and believe this is not within the NCR act aswell as treating clients fairly.

I need this be escalated or I will need to escalate to ombudsman upon outcome of this experience.