So you selected an available URL, went into Settings - Publishing, changed the address, and republished to the new address. Fine.
Then you discovered that you can still see the old URL. Not so fine.
What you did was similar in effect to someone switching to external publishing. Like someone who switched to external publishing, you can still see the old blog. Hopefully, it still has your contents there.
At one time, if you switched your blog address, or changed to external publishing, and looked back later, you'd likely find a splog sitting at your old URL.
If you gave up your mature and valuable URL, a spammer would take it.
When you gave up the URL, a spammer found out about it, and started publishing there. Splogs are designed to exploit that mistake.
Blogger Engineering tries - not always successfully - to block spammers.
But Blogger Support got tired of folks complaining about the splogs, so they fixed it so URLs that were abandoned, either from deletion or from publishing to a different address, wouldn't be available.
So now it looks like you have to contact Blogger Support, and explain the problem. And don't forget to reply to the botmail.
And in the future, if you change or delete your blog, plan the change properly. Put a stub blog in its place. But do this carefully.
Use a carefully planned script - written before you start.
Follow this procedure for migrating your blog to a new URL. Think about each step first, and do them in sequence.
- Backup your current blog, as it is now in Blogspot.com.
- Backup the template, into a text file. Save the backup file in several places.
- Change the Blogger settings, on your current blog, to publish to the new URL.
- Change the Blogger settings, on your stub blog, to publish to your current URL.
- Use a well planned script - and carefully swap URLs.
If I was doing this, I would do all steps at the same time, one after the other. I would probably not take a rest break, and I certainly wouldn't let the sun go down, before completing the last step. Seriously. Read Spam Blogs #3, if you don't understand how frustrating it will be for you to have to have your vacated blogspot address used for a splog.