Discount as advertised was not given

Mimmo's in Pavillion has a special: 15 percent off your bill if you produce a n?metro movie ticket which I happened to have. The food was terrible but I didn't think there was any point in complaining so we requested the bill and were given a comment card to fill along with it. I filled in the comment card but I didn't fill in my contact details because I didn't want to get unwanted emails or sms's. The waitress then took my n?metro ticket receipt inorder to give me the discount but returned having been told by the manager that we did not qualify for the discount. I'd like some clarity as to why we did not qualify for the discount advertised? I had 2 movie tickets for that afternoon.