You are unlikely to recover an over written Excel file. Basically files are saved in "data chucks" on a hard drive which is divided up into sectors. When a file is saved over, the "data chunks" are overwritten in the same sectors the original file occupied (more or less). The larger the file the more sectors are used, the smaller the file the fewer sectors are used.
To speak plainly, when a sector is overwritten with new data, the old data is gone.