If my return was rejected because it say my social security number has already been used , what does that mean? And what do I do to fix the problem?

Fix is file on paper.

See this

https://turbotax.intuit.com/tax-tips/security/identity-theft-what-to-do-if-someone-has-already-filed-taxes-using-your-social-security-number/L4NBQHSM2

First question is-

Are you a dependent? If someone else can claim you as their dependent you may still file (in fact you may need to) but you must file as a dependent. In TurboTax be sure to select "Yes, someone else can claim me" and "yes, someone else will claim me"

 

Are you NOT a dependent and someone else claimed your social security number for filing? 

Inform the IRS. 

Fill out Form 14039 

 You can print the form and securely mail it along with proper documentation or complete the form online.

The IRS will respond to you and investigate. 

 

Since you can't e-file, you may need to print and mail your tax return in, you still need to get that filed by the due date or apply for an extension (request for extension would also need to be mailed). 

 

You should do other things not relating to tax, such as freezing credit cards and safeguarding financial accounts. Contact the credit bureaus to report the problem. 

 

HERE is more details from TurboTax.

 

@jbsmith16