Only sitemaps submitted using Google Search Console and Bing Webmaster Tools are listed on the Sitemaps page within the tools. To make sure your sitemap information is visible, it's a good idea to use Search Console/Webmaster Tools to submit your sitemap for the first time, and then use ping (or robots.txt) to update it.
A successful request will return an HTTP 200 response code; if you receive a different response, you should resubmit your request.
The HTTP 200 response code only indicates that the search engine has received your Sitemap, not that the Sitemap itself or the URLs contained in it were valid.
If you are providing a Sitemap index file, you only need to issue one HTTP request that includes the location of the Sitemap index file; you do not need to issue individual requests for each Sitemap listed in the index.