Installmant raised without permission

I became a member a while back with a installment of R843 on my Toyota Hilux. Suddenly about 3 months ago the installment went up to R1398 without any notification or knowlede of any sort (no call or documentation received). I then contacted Discovery Insure multiple times (with promises that they will assist me and phone me back) but there was absolutely no assistance! I kept phoning back daily for about 2 weeks without any success. They then referred me to another department but still no response. I cannot even try to refer to the matter as poor service as there was absolutely no service to refer to!