Flipkart — Wrong mattress size suggested and delivered

These people suggested me king size mattress 75”X72”. But when I received and checked then I find it is smaller. My requirement is 78”X72” at that time Customercare told me we can change size later but now they are saying we can replace with same size. If I asked refund so that I can order it again some bigger size. But they are saying as per policy we can give you any refund. We can replace with same size if there is any defect. Now I am feeling why I ordered through flipkart. It is my big mistake. This mattress is not useful for me. Anyway I lost my money and mattress is not useful for me. Please don’t buy anything from flipkart. Help me in getting my money back.
Whenever I ask help from Customercare they always says they can’t do anything in this case as they are mediator between buyer and seller. Please help me in this regards.
They always prepare policy in there favour not in the favour of customer. I will definitely accelerate this issue to even court.