interest charges

After numerous attempts to settle my game account ( I was told by the call centre I needed to go in store but they always offline), I paid what was outstanding on the account by 30 oct 2017.

On 15 November I get a statement of money owing to the value of R 196.51 Collection fee /7 sms charges R64.41 (to the end of October 2017) then on 10th Nov Monthly service fee R55.00 Interest R6.26 Cust protection fee R4.00 Interest R66.84

I called the call centre and thy could not explain what the interest was charged against or even how it was calculated. on 15 Nov I called the call centre again an they logged call with admin who till today have not called me back. I called back again the Thursday 16 Nov but I was just transferred from the 1 centre to the other. on 20 Nov I sent a mail to ********** but still today no response.

All I need to know is how the interest calculation was done and against what amount was it calculated!