False Advertising of Vouchers

Pick n Pay send out vouchers for your top 10 purchases from time to time, i got this email in June which i thought was great, and used 3 of the vouchers on my next visit. A month later i got sent another email with some more vouchers, so of course i go to Pick n Pay to do my shop and when i go to the kiosk to claim the vouchers nothing comes up. So i call the call centre and explain what happened, and after holding for 20 minutes for the agent to find out what happening she tells me i already used the vouchers, they the same ones from a month ago? I then asked to speak to a supervisor, so i hold for another 10 mins only to be told the he's busy and will call me back! What a waste of my time!! And dont send out emails offering vouchers in July if you going to tell me ive already used them in June?! Thats false advertsing!! Ruined my day Pick n Pay, thanks.