Discovery Insure Premuim Discount

Discovery Insure advertised on TV and sent me an email and SMS stating that if I drive less than 500km per month I will get between 15 and 25% discount. In April my premium was discounted by 15%. In May I also drove less than 500km but did not get a discount. Called them and they stated it was only for April so I sent the proof of SMS and email. I was then told it would be paid back as part of my Fuel rewards but that did not happen either. I was given this ref no***