Outstanding loan amount dispute

I am writing this with sadness and disappointment on my face. On 2015 December I got a loan with Old mutual, for 12 months; due to other financial issues I could not pay this on time and my account was handed over, I was communicating with this company Vericred towards the payment, I then got a discount then decided to pay it off, this was around 2017/2018. In 2022 I got a call that I still owe old mutual an amount of R1243. 97 and I last made a payment in October 2021! And I was shocked, I rushed into the nearest branch and got the statement, the dates were recent, when I try to explain that they said but this is what we have! I am confused now because I don't understand why would it take Old Mutual 3 years just to discover that I owe them only R1243. 97. Someone clearly didn't do their job here and I'm taking the fall now. Please assist me anyhow because this is lowering my credit score rating.