Missing items and refund

So last night i decided to order some groceries on just eat, everything seemed fine until the order arrived and i noticed that quite a few items are missing.

I went back on the just eat app and i reported it as missing items as the items were not subsititued or marked as unavalible. I woke up this morning with an email saying the will not be refunding it. Obviously this is a bit upsetting and dissapointing as i paid for items i never even recieved.

Should my mext step be to raise a dispute with my bank ot should i try and fight just eat for the refund