At MAC Freestanding stores like mine, we are NOT allowed to process a return if someone doesn't have a receipt and/or if it has been more than 30 days.
If you don't have the receipt or it has been more than 30 days there is literally nothing we can do for you in the store, but all MAC Stores SHOULD be referring you to the 1-800 number for MAC Global Communications. They should be able to help you out and either do a refund or exchange if you can't do one in the store for some reason.
If you need the number, when I go to work on Thursday I'll write it down and post it here...