Allright since you no longer have the account that was used to create the posts you are not going to be able to delete it.
You could try and log into your old account but like I said if you did delete that account it may not let you as there is no way to re-activate the account.
I just checked it out some more and your profile on yahoo is gone so that is good.
Your only course of action I believe is going to be to get that post deleted from the group. This means you will need to try and contact the group owner and see if they can delete it for you . send an email to this address with the link to the post that says your name[email protected]
It doesn't look like the group is active any more so that could be a problem and I do not know if they will reply to you.
My advice other then that is to create yourself an email address that IS NOT Customer or anything similiar to that. That way it could look to employers that it is just another person that has the same name as you.
Another technique is to try and bury the information by getting more content on the web with your name so if anyone googles it , that will come up first. These could be a facebook profile, or a linkedin profile. Maybe start a blog under your real name or something like that.
The trick is to separate your self from that yahoo listing. So not using Customer as you did on this site is a must!
That even someone does stumble across the yahoo listing they will not know for sure if it is you or someone else.
You can try using this yahoo form to report that your personal info is being displayed. Go here
And fill out the form as I have shown in this picture.
Hopefully they will be able to do something for you.
Also after you are finished with me and click accept. i will send this question to customer service to block out your information so this question does not come up in google as well.