No Response to Queries Raised

Dear Sir, I recently expressed my concern that one always has to check ones till slip to ensure that the relevant discounts have been given. I have now been to checkers and quite a few occasions where the discount quoted was not given. I had to produce my till slip and the goods and the discount was then given. My quetsion is simple. Why should I have to check what checkers is supposed to be doing in the firstplace. If I take the goods back later it costs me quite a bit in petrol to do so.