Dollar General review: sale of purchase

I shop at store #14913, I went today 03/13/2016 make a purchase of the cereals on sale, 3/$6 I had raisin bran, honey bunches of oats with almonds, and froot loops, it run up at normal cost I ask about the sale and I was told I couldn't get it like that had to be the same cereal couldn't mix them, I had him to remove it from my purchase so I didn't purchase them, I have always mix them before at the other store. The worker didn't even care to try straighten it out, I went called another local dollar store in ask it was like I said I should of been able to purchase them like I tried, with a line waiting to check out it made me feel bad like I done something wrong