Fully settled an account but account still not closed

I asked them to give me a settlement amount so that i can pay it by debit order, they did so, i then settled my account in full November 2024, December the company i was owing kept on reminding me that my account still has to be paid, i alerted nimble and they said i should not worry my account was indeed paid in full they will send a paid up letter, each and every month till to date( March) my account has not been closed, it has accumulated arrears which are amounting to almost R1500 now and they keep on saying they will sort it out