It's most likely a "view" problem. Is your site live somewhere?

Can you send me the direct URL to that date listing in the frontend please?

Use our contact form: www.joomlaworks.net/support/get-help/contact

Check the language strings, perhaps there's some weird setup there for your language pack. The data seems correct. Append ?format=json to both the URLs you sent me and you'll see the date is correct.

So in other words, the raw date is not translated to the right language string. Look in the language files, look for any language overrides and finally, check your K2 overrides (if there are any). There might be some weird "month + 1" output for some reason...