It does seem to have been deleted: there's no way of knowing why without being able to look at the feed, but one would assume that it doesn't contain the sort of unacceptable material which would get it removed (unless perhaps it contained strong language when no 'explicit' tag was set).
You could try emailing them at podcasts 'at' apple.com but they tend not to explain removals.
If you want to resubmit you will need to change the title slightly to avoid the irritating error message you've encountered. You can always change it back once accepted provided doing so does not change the feed URL.
The XML is fine: http://www.themotts.ca/podcast/podcast.xml
I actually tried renaming the xml but still got the error message that I had already submitted that feed.
And The Motts content is very family friendly.
I'll write that address. Thanks again.