I've never had luck with the sprays. Buy cat scratching posts. The cardboard cat scratching posts do not work. You want the sisal rope one (assuming your cat won't eat the stings sticking out- I have one cat who loves to eat the strings), or one of the carpeted ones.
Or you can pick up dollar store door mat's. The cat's may use those instead of the carpet. Scratching posts are best though!
The trick is offering acceptable alternatives to the door and carpet, preferably more than one, because each cat has its own preferences. Try both vertical and horizontal surfaces - a scratching post or better yet, a tree (usually sisal or carpet), scratching mats (rough doormats, carpet samples or the like) both lain flat and tacked to a vertical surface, cardboard scratchers, an old chair (many people believe that will lead to scratching all furniture, but that hasn't been my experience).