How To Open Generated Xls File By Ptpexcel Extension

I have used to generate excel file and its working.

but there is problem when i just download/open it .

when i save the file on my computer prior to open it, it works, but when i just download/open it, it frozes!

file name is change when i download/open it e.g test.xls.xlsx

how can i just download /open with this extension