Exchange without a slip!

I have a brand new item with the tag/sticker on it which does not fit & I would like to exchange it for a size or another item but apparently this cannot be done without a slip due to their systems been changed in September? Which has not been notified to their customers with regards to purchases done before September & I have done this many times in the past without a slip to exchange an item as which other store is going to keep the rage brand? This is very disappointing as a rage customer that has been purchasing from this store for many many years as well as could of assisted this time & make it known to their customers to please keep their slips in future! Please advise? Thank you