Increased installment

I purchased a dodge calliber in 2012, I was financed by Absa vehicle finance, I have been paying the same instalment since I purchased the vehicle, in march 2015 I got a statement from absa that I must pay R900 more because I don't have insurance on my car, I told them that I do have insurance and I even emailed them my proof of insurance, my problem they never called me to find out if I do have insurance or not, if they did that I was going to inform them that I do have and send them proof, they say I must still pay R900 more for this month (April). now I must pay my insurance R900 an another R900 for absa for insurance that I have.