Bank charges on credit card

I am very disappointed with Standard bank .My account number CREDIT_CARD *** .On the 04th Augustus my outstanding balance was R308.31 I Deposit R300.00 Balance WAS R8.31 on the 04 August my new balance was R68.31 what i don't understand is from R8.31 to R68.31 .On the 05 August i made a payment of R80.00 and on the 6th August my new balance now is R48.31.

Can someone from standard bank help me to understand that math's because I don't

And why is that the account jumps from R8.31 after payment of R80.00 tot R48.31

I'm very Disappointed with standard bank .

Need answer because i want to close that account