Refund on short delivery not received

We ordered & received an invoice for 2000l of biodiesel, which we (promptly) paid in full. Take note that the supplier pushes for payment & don't even start arranging delivery before payment is received. They firstly took their time delivering, although we said it's urgent & we had to follow up numerous times as the days past on which they said they would deliver & then didn't. Then only 1917l was delivered. They kept quiet until we raised it. They only rep**** after numerous communications that they'll sort it out. That was 19 Feb & we have not been refunded & they are not responding again to all the communications.