Ymail.com, AT&T and third party billing

My AT&T personal phone bill is getting slammed with invalid, fraudulent, third party billing.

AT&T are quite nice about correcting the errors.

AT&T has traced these to [invalid names]@ymail.com.

They say that even though my account has third party billing blocked several are somehow getting through anyway.

They say that many senior citizens who don’t even have a computer are getting billed for an odyssey streaming radio monthly fee.

We are cooperating with AT&T and the state Public Utilities agencies who investigate these things.

Have you heard of this? Do you have any additional ideas as to how to stop it?