Settlement letter nightmare and additional fees.

On the month of Jan i finished my Truworths installment, i requested a letter and an agent said i still owe R150 for admin of which i gladly obliged. Months later i am told i owe about R600. I feel cheated because no one called to communicate this to me until i phoned. their consultant went on to say a supervisor is in a meeting and will call back tomorrow that was last week on Monday. My bank details have never chanced, no debit order has bounced, i have received my salary on the same date. i feel as if they did not debit so that this R150 can accumulate interest and they can get more money out of me hence the poor communication.