On contacting Yahoo Customer care, does that mean you called them?
Check out http://www.contacthelp.com/directory/Internet/Web+Sites/Yahoo?ListingID=148
I know you created accounts other than Yahoo but if you really want access back to the important Yahoo account, try to create another Yahoo account and work with customer service from there.
--- Once you are all set, you can continue to use your important and new Yahoo accounts if you wish
--- On the alternate Yahoo account you already have, you can address that one also or just let it "expire"
------ If I remember correctly an unattended Yahoo email account is deleted after 3 months of not being used
What I have done a few times this past year for a couple of friends is I had them send a message to customer service regarding their issue and in each case I believe it took at least 2 weeks to get a response.
--- On my of my friends account, Yahoo support worked out fine but he had to respond to I believe 4 messages before someone got it right to help him out
--- On my other friend, well he just didn't bother and he's happy using gmail
On Yahoo help central, generally speaking that's more than a challenge to wade through and find help on what your looking for