simple sitemaps sitemap.xml turn into html format

I'm using a simple sitemaps plugin in my multiple site network right now. But for some reason, /sitemap.xml is converting into html formate. Please help.

so display in this format

http://www.domain.com/ 2016-03-15T17:04:01+00:00 1.0 http://www.domain.com/physicians/ 2016-03-18T20:31:08+00:00 1.0 http://www.domain.com/services/ 2016-03-14T21:40:04+00:00 1.0 http://www.domain.com/resources/ 2016-03-18T20:01:51+00:00 1.0 http://www.domain.com/forms/ 2016-03-16T17:24:34+00:00 1.0 http://www.domain.com/contact/ 2016-03-18T20:31:15+00:00 1.0 http://www.domain.com/alert/ 2016-03-16T17:27:53+00:00 1.0