Defective Oxford corner unit

I purchased an Oxford corner unit in December 2014 and the cushioning is sinking to the point where it touches the base of the sofa and is very uncomfortable to now sit on. I went twice to the gateway branch and spoke to the store manager who had advised me to send her an email with the details and a picture of the sofa. I sent that email 3 weeks ago and have been following up and have had no response from anyone as yet. I did pay a lot for this sofa and expected good quality and what's even worse is the terrible customer service. I have been purchasing most of my furniture from @home and this is the first time I actually have a complaint. Please assist urgently