After I saved an Excel document, I remembered that I needed to change something in it, so I go back to open it and it said

Excel cannot open the file, because the file format or the file extension is not valid. Verify that the file has not been corrupted and that the file extension matches the format of the file.

I know when I saved before, around 2hours ago, it worked just fine. The document size is at 0KB now. How do I recover this document? Its crucial for my business!