someone with sense talk to me and close account

I went into the branch to ask for my credit cards to be closed,I was told it would take 48 hours and then if there are no extra costs it will be closed.Yesterday I get a call confirming closure of one card and I am told the second one cant be closed because I owe interest on the last two purchases made,<br> Question 1 since when do I get charged interest for purchases on the credit card<br> Secondly how do you justify interest of R305(the amount I am told I have to pay) for purchases totalling R 275<br> The account that I want closed is in credit of R73 how do I then owe money on an account in credit.<br> This is utter nonsense<br> I want the account closed and I will not take responsibility of any bank charges on an account that is being kept open over stupidity.