Sold expired food items

I bought a pack of chocolate digestive biscuits and twizzlers few days ago. Paid full price for them. It was for my niece and nephew. Their mum calls me to say the stuff was expired long time and one of the child is having a severe tummy pain and running tummy. I phoned melrose arch flower market and the lady who spoke to me wasn’t apologetic, instead said calmly “we can only refund you for the items that haven’t been opened” The digestive biscuits where expired since 2018 and twizzlers since September 2020.. and she says she is inward of the expiry! A 2 years expired product that wasn’t even marked down and all they can do is refund me for an unopened item!!