Poor service. Overcharging premium

I am a member of discovery health. I am. On the keycare option for me and my son. I had to fill in forms to confirm my monthly income just to find out that my monthly premium has increased with over R600 a month. My salary bracket only increased with R300. I am a single parent and cannot afford an increase as much as that. I have never had to send any income verification forms and I would like to know how they get to their figures if they don't even calculate your monthly expenses.