At this point if you have not tried to e-file a tax return then you probably will not be able to e-file anyhow---the system is getting ready to switch to 2020. Print sign and mail your tax return. If someone else used your SSN on a tax return, the IRS will sort it out. Just file your own tax return correctly, and let the IRS worry about what your ex might have done.
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.
Federal and state returns must be in separate envelopes and they are mailed to different addresses. Read the mailing instructions that print with your tax return carefully so you mail them to the right addresses.