Taking Just Eat to court

I've absolutely had enough of their shocking customer service after yet another order where half the order was missing and they've not replied to a single message ive sent them asking to sort out my money. I will literally take them to court over it whether people think its not worth the stress or not because they need to stop stealing money then thinking ignoring you is the way to go. Does anyone know what contact details I can use to send them a letter before action and final warning to as I cannot find any contact details for them online and as I said they haven't replied to my messages via the contact Us page on the app?