Sometimes a SSN gets typed incorrectly by a random stranger; sometimes a SSN gets used by another person deliberately---- no way to tell now. But if your return is being rejected for an incorrect or "already used" SSN, the only way to file it is to print, sign and mail the return. You cannot e-file it. Sorry.
When you mail a tax return, you need to attach any documents showing tax withheld, such as your W-2’s or any 1099’s. Use a mailing service that will track it, such as UPS or certified mail so you will know the IRS/state received the return.