We get an occasional odd report about a blog, recently setup with a custom domain using "Buy a domain", which cannot be accessed using either the BlogSpot or domain URL. Upon investigation using a Whois log, we see an odd detail.
An HTTP trace will appear identical to an improperly published domain.
Upon further discussion with the blog owner, we also learn that the blog owner has seen no charge against the bank account provided for the purchase process. The only sign of the purchase is the BlogSpot URL, redirected to the domain URL.
In this case, the only choice is to publish the blog back to the BlogSpot URL, then repeat the purchase, again using "Buy a domain" - but after diagnosing and possibly correcting your credit card information.