Increasing the prices at the paying point

So game tired to play a fast one on me today.

Went in to buy a few things from game, then I paid for the items which cost me about R178, and on my way out I started double checking my slip and realised that what was charged on the slip is not was what I saw when I took the items. Went to manager and asked him about the price and why they overcharged me so much and no valid explanation was given to me...... My problem is that had i not noticed that I paid extra they would have never said nothing. I asked for a refund they kept me waiting there as If I was out of mind and when they did finally refund I was told to wait in line to get my money back. Who the hell does that????? Got me thinking how many of us are they doing this too.