Trying to close my credit card

I have tried numerous times to close my standard bank credit card and each time there remains a outstanding balance a few weeks ago I called in after I have settled my account just to be told that there is still a outstanding amount. I told the call center clerk that I will make payment and she should close the account as I will not pay any more. This morning I received yet another mail stating that my card is over due. So my card was not canceled. I now again made a payment settling the amount and this is now the last payment which I communicated to then via email. If they don't want to cancel the card we'll F@#& it I am done they must hand me over. I have proof that I tried to cancel the card but they seem incapable of doing so.