SERVICE FAILURE BUY CLICKS

I recently purchased a pack of 48 Disprins from Clicks, Mall of the South. These were on special promotion at the time. On checking the slip when I got home, I saw that I has been charge R93.99 (the normal price) instead of R78.99 (the promotion price). A few days later I called at Clicks, Glenvista and requested that this be corrected. I was told that I had to return to the actual store where the purchase had been made and they could not help me. The problem arises that I have to pay R10 parking fees to go back to the store at Mall of the South. Really disappointed that an organisation as large as Clicks does not assist customers not matter where the problem is reported.