The store agree to refund you. So you have no loss.
Most products has no written expire date.
I once take to county health department about similar problem. In United State, even cigrate can be for sale to public, it is proved to harm to human health. If you can not prove it is harm to many people, not just you. You may not have a case. If you loss in court, you may need to pay another side attorney fee as well.
The store already agree to refund you. what you want?