Credit card confusion

I'm having difficulties with my credit card, one day there's an available balance next few days the balance available is R0,from Tuesday my available was R0 then suddenly my balance yesterday(28/09)was R370 in I used R120 today when I wake my balance is back to R0,I'm so confused,on the 20th I put R870 plus my debit order for R869 went off yet my balance was R0 then few days later it went R780,I called the centre 4 times today and could not get assistance each agent tells me something else,the first agent told me to check my transactions on the app and if I have a problem I should call back,and if I calculate my transactions on the app I'm actually suppose to be in a positive of R689 . I need someone to thorougly investigate what's happening cause this is a mess,and why is the app and credit card not corisponding.why does the balance change daily and over night,and how does my available increase den decrease automatically