I've got a new WordPress website that I'm testing that hasn't been updating properly when CSS styles are updated over FTP. I haven't got a cache plugin and I have cleared my browser cache and have tried a different browser. The changes I make are definitely being uploaded to style.css as I have downloaded it and checked it on a web FTP site. I can tell the code is not wrong because I have copied it to a new file, included it in header.php and it has changed. Also, when I delete style.css, the styles on the page do not change.
I've checked my HTML a hundred times and I'm not including other stylesheets and making huge obvious changes to styles doesn't do anything either.