Big Lots Rip off , Internet

Big Lots, Greenville, SC    I went into Big Lots to purchase Christmas Lights.  In there add, it was stated if you spend $50.00 you would receive a $10.00 store credit to be used from 11-25 thru 12-08.  I purchased $281.78 of product, total of $50.00 in credits.   When I went into Big Lots to redeem my credits, I was then told that I had only $10.00 worth of credits.  I spoke to two assistant managers and they called the store manager on the phone, but still no one would honor the correct store credits.  I was told to call the store when the manager was in or call the corporate office and voice my issue.  This is one big rip off and this store is not honoring their newspaper add.