Even if it looks like the module is installed, as far as Python is concerned it isn't since it throw that exception.
Try installing the module again using one of the installation methods shown in the XlsxWriter docsand look out for any installation errors.
If there are none then run a sample program like the following:
workbook = xlsxwriter.Workbook('hello.xlsx')
worksheet = workbook.add_worksheet()
worksheet.write('A1', 'Hello world')