Game charges even if the account is paid

Hi I have paid the full amount on my account *** and it had a zero balance and now I get statement that I have to pay R67.62 and the consultant I spoke to told me it will be more after 5 days why am I being charged interest when the money i owed you its been paid up? I was told if I pay it off I wont be charged unless if I buy, that's unacceptable I wasn't made aware that I will be charged even if my account is paid and I would like to close the account please am not accepting the day light *******