Refused double the difference

Yesterday I purchased a coconut that was marked at R8.99 on the shelf but scanned as R14.99 at the till, I pointed this out to the cashier and she called someone to check the price n the shelf to verify. She found the the price was R8.99 and called a superior to correct the price on the till. When I asked for double the difference (In this case R12.00) to be refunded to me, the superior (Arnold, I may have the name slightly wrong) rudely said no, it does not apply to fresh produce. However there is no mention of this clause on the sign in the store or on the website [URL Removed] This is very disappointing to be **** to considering that I have been a very frequent pick n pay customer for the last 5 years.