Interest Charged completely unreasonable

Good day,<br> I am deeply and terribly upset. I paid 60k towards my discovery credit card at the end of Feb, on which I owed 62,100 rand at the time. I was unaware of the fact that if you do not pay the full amount that I will be charge interest on the total amount. How on earth does that make sense? I paid 60,000 rand!!! owed you 2,100 rand and you charge me interest in 62,100??? How can you possible justify this? The call centre said it is the rule of the cards, I think it is unfair and a completely unreasonable practise. If I knew I would of course paid the teeny tiny little amount now instead it cost me 1120 in interest. I am so frustrated.<br> Thanks<br> Bianca