Terrible matress

I bouggt a bed 3/4 years ago. It has gone back 3 times because the bed made a terrible noise everytime I turned or moved. ItsI a none turn matressit. I had gone back to the store numerous times after complaining that the bed was making a noise again. Keep being told a manager will call me. The noise is worse than ever and bed is slanting to the middle again. I weight 50kgs and suppose to support over 100kg. I am now pregnant and cannot afford a mattress with no support and being woken up everytime I move. I paid a lot of money for a bed thats suppose to last 10+ years but this bes is not lasting at all!!