H&M exchange standards

I'am dissapointed and confused by the H&M clothing store at Mall of the North for their apparent rule that cannot offer an exchange for a product bought thats still intact , still has barcodes and never worn. My wife bought a denim for R629 and lost a slip so now she's stuck with a denim that doesnt fit - The staff in the store are powerless and cannot make these kind of decisions as they were given strict instructions by their headquarters. I don't see the sense in this policy nor see why the store believes they are doing customers a favour - the policy must favour customers first then the business - I see this a bad customer service and complete rudeness and lack of consideration especially during these tough times.H&M must put on their thinking cap.