Holiday leaves Bad Taste

I booked a week at Goudini on the 3rd June 2015, on behalf of my parents , the stay was from 12- 16 October 2015.They sent through the confirmation of the booking and had added a 10% senior discount. A week before my parent's trip , I called to find out if their any outstanding monies, I was told R47, which was 100% correct. However upon arrival my parents were told that they still owed R297 on their booking. They paid it, but asked me to look into it. It seemed that they didn't include the 10% discount THEY HAD OFFERED, I tried calling them about this and was given 2 different excuses as to why it was given and then excluded I asked to speak to the manager who didnt bothered to return my calls .I eventually spoke to her (she claimed to have tried to call me but I have no missed calls on either my landline or cellphone), and said the person who had made the mistake no longer works there and that my parents did not qualify for the discount, as they not 60 yet. Yes they not but the booking was made on my mom's ID and she was never 60 so that discount should not have been given in the 1st place, as the mistake was on their side and they had 4 months to notify us of mistake, but didnt