Refuse to replace my item at the same price I paid

I purchased a pair of jeggings at your clothing store At west coast villiage on the 5th July 15 and the stitching is coming loose on the side so I went back yeaterday to REPLACE with the same jegging. When I purchased it it was R70 now the price has gone up to R139. Your teller and assistant manager refused to replace my item at the same cost I paid!!! It is not my problem that the defective product you sold me price has gone up! You are supposed to replace the exact same goods at the original purchase price!! Never mind the fact that the staff were incredibly rude and unhelpful! Are the public aware at how pnp sell defective goods at a low price and then demand you pay in more money on return? Is this your way of making extra money from the public?