Disappointed

I have an account at rage which I'm owing 315 their instalment keeps changing without being notify about the changes, worse they don't produce monthly instalment letter as other companies do, last month I paid 50 last because of not know how much I should pay, and later was told that I'm owing 36 rand and ok may I paid 135 rand so where am I owing them that they affect my credit score saying I missed payment which payment did I miss, I'm so disappointed with rage I work so hard to build my score and they come with this. Can they tell me the total amount I'm owing and close this account forever