AMPATH ACCOUNTS - can't recon their own accounts

I paid an account in December 2019 using one of their payment options on their statement and received confirmation from that service provider that the payment was successful. I received an outstanding account statement from Ampath in January 2020 - I have since contacted their accounts department 4-5 times, sent them proof of payment 4-5 times including a snippet of my bank statement proving the payment was made from my account and they STILL HAND ME OVER TO A COLLECTION AGENCY!!!! I have been using their services for 2 years now (their Life4Ways lab staff is brilliant) and between medical aid and myself have settled accounts for approximately R70k...yet they dispute a payment of R162.00...AMPATHETIC...