Refuse to refund

I ordered foodstuffs on the 23rd March, it was only delivered on the 30th March however less than half was delivered. Since then I've been trying to get a refund on money paid but nothing, its been over a week and they still refuse to credit me!!! It first took a week to deliver 2 packets of food and now they have decided to keep my money!! What an *********** lot, I want my money back or deliver the goods I ordered.