Unprofessional

I have settled my account on the 28th of February, everytime I ask for my settlement letter I am being told my account is in arrears with R500, which I don't understand because my first payment was R500 on the 28 of January 2023 then my last payment was 28 of February 2023 I have sent all the prove of payment but they still can't see the 1st payment I made & sent prove of payment, how possible is this? , today they tell me they can't open my file they are so unprofessional