mislead through insuffitient information

tiles fell from the roof top causing damage on my boot and bonet as well as wind screen, after submitting my claim Miway informed me of something I never was made aware of ,that my claim access will be R20 000 for any damages to my car, if the claim is less than R20000 then they will not cover me, if the claim is R25000 I will have to pay R20000 and they will only pay R5000, no person in their sober mind would have agreed to such terms, I took this Insurance over phone line and at no point was this issue mentioned otherwise I would have looked for a better insurer,I have since been waiting for the ducuments from them to sign but have received nothing so far, I am really stressed