Unpleasant service

My friend and I had won 3 coupons from Vodacom shake everyday. We visited Kauai in Cape Town a guy came to the till we advised we had coupons. So he went and got what we assumed was the manager. She came with to the till with a very unpleasant face. We gave her the phone she scanned the coupons and then we got our shakes. The shakes were awful!!!!!!!!! So since I have a friend who works at Kauai but at a different branch I told her about this and she said that isn't how our shakes were suppose to be done. I mean it was basically 80% ice. I'm not sure whether they did that on purpose since we had coupons - however I would think that they should claim(whatever their process would be from) Vodacom. That is very bad for business because had it been our first time getting shakes from them we would definitely never return to any branch for that matter not only because of their service but also because of the ice filled shakes they made us.