Jeans Size Disparity

Bought my 3rd pair of Ranger slim fit black jeans from Kingsley Heath in Rosebank. My previous 2 pairs were exactly the same size/style or let me rather say supposed to be the same. I took the jeans to the tailor to adjust the length straight after buying them like I always do. When I tried the jeans on I then discovered that the new jean measurements/cut is not the same even though the description on the jean is exactly the same as my previous 2 pairs. I did not bother to try the jeans on when I bought them as I knew exactly what I was looking for. The manager at the store said that I must return the jean. I returned the jean and also took an old pair with to show them the difference. I was then told that they can't assist me as the jean has been altered. My opinion is that I was misled and that the necessary quality control measures were not in place when the store took in new stock.