Lifespan of a calculator

I purchased a Sharp scientific calculator the 14th of January, when the back to school promotion was running - this is done every year. However, since then certain buttons on the calculator doesn't work at all. I then thought, well my son hasn't had the benefit of said calculator for year so surely the store would have no problem swopping it. I called the Parow Mall store and was told although I don't have my slip any longer, my bank statement print out would suffice. Today I made my way to the mall and the manager informs me he is not willing to stop it out as he spoke to the regional manager who told him not to...I mean come on - so checkers hyper sells calculators with a lifespan of under 1 year? Please add this to the packaging when marketing the product. We live in tough times and passing the buck this way just adds to our deteriorating society...