INTEREST ON SETTLED ACCOUNT

Why is it that i have being paying interest on a no balance account for the past couple of months. i go to your credit desk and I stand another +-2 hours waiting for head office to answer the phone, because i as the client, must be at the phone and i personally, must let you know every time after i have cleared my account that i want a 0 balance and my account is not to be closed. i feel i have paid my account up so why does GAME CONTINUE TO CHARGE ME INTEREST on the account m.i. da costa