Don't seem to want to honor advertised discount

Alexander forbes newsletter advertised a 15% premium discount (on vehicles) if you pay your insurance a year in advance. I decided to take this offer up and advised the consultant of this. The annual premium was then calculated but I noticed that the \discount"didn't amount to the advertised 15% I queried this with the consultant who failed to get back to me on the issue. I then followed up again only to be told that the \""actuarial team confirmed that the discount is correctly calculated\"" Which is surprising because I would have thought that any matriculant with a calculator would be able to easily determine that the calculated amount of discount on the policy was closer to 5%. I then requested to speak to the head of customer service"