Descending bed

Good day, I bought a queen size bed at Sleepmasters South Gate branch. Date: 23 March 2020 Time16:01. The bed is not even 3 months old and its descending to the middle. Which is very uncomfortable myself and hubby as its affecting our backs and we not enjoying a full nights rest. I have logged a in May 2020 complaint reference number: SM-SLEE-*** and Customer ID- *** which to this day I haven't receive a phone call, email or sms stating that they looking into my case nothing. It was no hesitation for my to pay for the bed cash in full but its a problem to receive feedback. This is pathetic service, I want my money back they can fetch the bed I go somewhere else where my business is apricated.