You don't have a lot of options, but before I mention what they are, it's helpful to explain why everything you tried so far hasn't worked:
When you create a question or answer on Stack Overflow, you cede some of your rights under the Creative Commons license you were required to accept to publish new content.
One of those rights is the ability to cease distribution of your work provided the distributor meets all the criteria of the license. The benefit is that the community can rely on content remaining there for posterity.
That is, in exchange for others helping you (or you gaining reputation), what you publish on Stack Overflow needs to remain accessible as a resource to others who need help.
So your only real option is to e-mail [email protected] and ask them to disassociate your account from the question (this might actually require deleting your account). Your content stays, but you would at least no longer be associated with it on the live site.
But realize what happens on the internet in public stays on the internet in public. Even after any action is taken on your account or question, there are months and months of archives that still have the association between you and the question. It is likely that it will never go away.