Kurl - On — Florentino double bed mattress

I purchased a FLORENTINO DOUBLE BED MATTRESS for Rs 31699/- from Ladies corner xclusive, Chandigarh on 28 Jan. The same sank more than 1.5 Inch in the centre within 10 days. I complained and they replaced it on 21 Feb vide their invoice number[protected]. But within 15 days this also sank more than 1.5 Inch. It has led to me and my wife having constant backache. It shows the poor quality of the materials and also defective engineering. I have complained again on 14 Mar vide complaint number 10473757. They are insisting on replacement again. I want a refund. How many times we can suffer the inconvenience