Require Refund for the Bed Set

I bought the King size bed set in July 2015 but within three months of time the mattress is going in and we having back pain every morning, when i reported they told me to change the base set nothing wrong with Mattress but both i bought from them and are faulty, but till now i am battling but no positive response, now i just need refund as it got 3years guarantee and warranty for 6years i think.