If the carpet cut off method doesn't work try the cardboard scratch pads/mats. Our cats love cardboard. You can get them quite cheaply off ebay or more costly at PetsatHome. They do get annihilated after a while and can be a bit messy but we tried them after our cats started scratching the new carpets, especially a step on the landing, and they worked immediately. We just placed them where the cats offended the most.
Also, if your cat is quite large, an average scratch post may not be tall enough. We have a bottle raised feral x Maine Coon (you may recall the tales of the golden nuggets I posted on here a couple of years ago) who is now a really big boy and won't use the standard scratch post. I decided to invest in a taller one and all 5 cats prefer to use it as they can get a really good stretch on it.
Just some of my thoughts.