Do you have a server managing this saved file for you? I don't think you can (or should be allowed to) save files on a server or computer using Construct.
It sounds like your file is not getting saved, and thus you get 'stale' data from what your file actually contains.
You say you have a webserver (like Apache?), but Apache only delivers content. It does not manage it. You have to build an application of your own (in something like Java, PHP, Python?) to manage the files for you behind the scenes.