What do you mean by "saved a chart as a template"? Do you mean that you saved the Excel workbook as an Excel Template (*.xltx) or Excel 97-2003 Template (*.xlt).?
What apps are you trying to open it with?
If you want to create a new workbook from such a template, use File>New and select the template. When you do that, the workbook that is created will have filename with a number appended to the name of the template.