My ex-roommate has received both of my payments. I need to figure out how to stop my money from going into her account.
File a police report for theft of funds.
Notify the IRS, state, credit bureaus, etc. re Identity Theft as well.
If any of this was done through the mail, also file a report with the Postal Inspector.
The police won't do anything.
You can report fraudulent Tax Returns to the IRS on a form they supply for that purpose.
The only way to get your money is to file a correct return for yourself on paper. IRS will investigate the conflict.