Discrepancy between Cresta and Hillfox McDonald's on their food products

I wish to make a complaint / enquiry about McDonald' s Hillfox regards to their prices of their items mainly the 2 x ice cream cones and 1x XL fries. Yesterday at McDonald's Cresta, I bought a friend and myself an 2x ice cream cones and it came to a total cost of R9.80 = R4.90 per ice cream cone. Now, today, for the exact same ice cream cone and the same quantity of at McDonald's Hillfox I paid R12.00 for 2x cones which works out to be R6.00 each for an ice cream cones. The difference between the two stores for the ice cream amounts to R2.20 .I also paid 23.50 for XL fries where as the last time I bought fries at Cresta it was R22.00. What I cannot understand is how McDonald's being a franchise can have different pricing for their products. For me it is very suspicious and when I confronted the manager of the store at McDonald's Hillfox about the discrepancy I was told a story about how McDonald's Cresta maybe undercutting their prices to draw customers. Will all the *******ion in South Africa it is impossible to know what can be going on and so this is motivation for my review.