Poor quality linen

In January 2021 I purchased some double bed sheets online from Woolworths. Over the months of using the sheets, they became increasingly "bobbly" to the point that it is actually very uncomfortable to lie on them as it feels as if you are lying on sandpaper or crumbs. When I approached Woolworths I was told that their quality policy is 6 months and if not reported within that timeframe they cannot assist. A period of 6 months should not apply to linen, which is an item one purchases to last a long time, and in less than a year these sheets are unusable. I am not asking for a refund, rather an exchange, but Woolworths will not see reason. I have other sheets purchased from Woolworths that are 5 years old and still in excellent condition. Their stance on this matter is entirely unreasonable.