Make sure to contact Podcasts Support rather than the normal Apple Support, who don't deal with podcasting. Go to https://itunespartner.apple.com/en/podcasts/overview and click the 'Contact Us' link at the bottom of the page. If you can get them to describe the nature of the problem post it here and I'll have another look.
Incidentally, CastFeedValidator, Podbase, and FeedValidator all pass the feed as valid, though it's suggested you should add a sub-category to your category. You should choose from those in this list:
https://help.apple.com/itc/podcasts_connect/#/itc9267a2f12
However this in itself shouldn't cause the feed to be problematic.