Does one atonement for an oath, or three atonements, become binding on me due to breaking an oath to abstain from masturbation in Ramadan? And does a late atonement become binding on me for losing the fatwa number, and what is the late atonement?

Masturbation is Islamically reprehensible and invalidates the fast. It necessitates making up for the days on which semen was emitted. A single expiation for a broken oath (kaffarat yamin) is required for violating the oath; it is immediately due and must not be delayed. There is no expiation required for delaying the payment of the oath's expiation, but rather repentance and seeking forgiveness.