staff does not know how to process coupons/voucher

About a month ago, I had a problem with cashiers not knowing how to process unileverdeals coupons, was then contacted by a women called leana, I think she is assistant manager or in charge of customer care? She told me that she would inform her staff about coupons, I directly asked her if they know how to use \snapnsave\" wicodes, since I wanted to use it in future, she said yes. Yesterday when I tried to use wicode, supervisor just told me that she doesn't know about it, I then requested that they call leana, who then told me \" sorry code is to short\" without entering it at the till, I then askec them twice to please just try and enter the code I had since I knew it was correct. When they entered it, it worked. But why employ staff that does not have the common sense to enter a code and at least try it? They got very rude when the code worked, will never shop there again! "