Over charged on the account.

I have a problem paying truworths during the lockdown period so I have explained to them that I don't have enough money to pay my account. They said it's fine I must just pay the amount that I can afford. I did as they were saying. But now I see my self having ereals on my account. Pls help me to solve this problem. Because I had deficulties on pay the account because of the lockdown. Now they are charging more money every month I go and pay the account. The money that I know that I suppose to pay is R460 in this month of June. But my statement is showing R530.