DO NOT KNOW WHAT THEY ARE DOING

I got contacted pertaining to an Isabella Garcia account R1478.03, I paid 18.05.2021 R500.00, 25.06.2021 R500.00 and then I asked for a settlement amount which they told me R478.03 which I paid in full on 21.07.2021. PROBLEM, now yesterday got an email stating that I need to contact them urgently pertaining to my outstanding account. I have asked for a paid up letter 21.07.2021 and still not received. How do they operate as the first person that sent me the settlement is the same person sending me harassment emails that I have not paid. What do I do now... They read my emails. DONT RESPOND BACK