All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.
It is incumbent on the oath-taker to offer expiation when he breaks his oath. No expiation is due if a person claims to have sworn an oath when he actually did not. This is a lie, not an oath. In this case, the person should expiate for his sin by seeking forgiveness from Allaah The Exalted and turning to Him in repentance.
Allaah Knows best.