Debit our account after termination of service

Service was disconnected on 31 August 2022. Payments done upfront. They debited amount on 1 September 2022 of R499. 00. They cannot give proper explanation, even though we have proof. We spoke to 3 client service consultants. All 3 gave different reasons. They refuse to refund even though we have proof. Last consultation promised to email their proof, but we have not received till date. Please help...