Card cost £22 and is 16gb. It's from a reputable retailer. What has the phone done to it and can I get it to work again?
If it showing up as bad in a PC as well as the phone, it's probably kaput. I have had 2 sd cards go bad in phones, one in a ZTE Blade 3, one in a Motorola Moto G 3rd gen, they do sometimes die. One was from Currys Digital and one from Maplin. Because I had kept the receipts, I took them back and got my money back.
You could try formatting it in a digital camera.