Swiggy — Product listed in bill not delivered

I had ordered food 3 burgers and french fries. After the bill is placed, since missing 4th burger. I contacted swiggy via chat to place order and they confirmed via msg to pay the amount for the 4th burger by cash to delivery partner. I did so and after checking the item, the 4th burger was missing. When I asked the representative they said 180 rs will be refunded for the bill of 229 for their mistake.