You probably forgot to close it. Use fclose(). Or fclose all.
I don't know what write method you're talking about. This is all I have
Write data to remote host over TCP/IP interface
Does not sound like that's what you're referring to. If you're using xlswrite, MATLAB 22015b and later keeps Excel open to your file, unlike prior versions, so trying to delete the workbook may not work since you can't delete a file that some process has open and locked. Some programs, perhaps Excel, will place a lock on the file, and some programs, like Notepad, don't. Perhaps fclose('all') may fix it - I don't know. If not, you'll have to use actxGetRunningServer() to get the handle to Excel then quit Excel
hExcel = actxGetRunningServer('Excel');
or something like that.