Call customer support and ask for the security team.
https://ttlc.intuit.com/turbotax-support/en-us/contact
It seems likely that someone made a typo when setting up their account, and they are typing in your user name by mistake, and trying to reset their password. I don't think there is much way of stopping this short of contacting them directly to clear up the problem. So you need to call the security team.
