Praise be to Allah.
If someone swears not to do something, then does it, he must offer expiation for breaking an oath (kaffaarat yameen ). That is obligatory.
If he swears that he will not break his oath, or he swears that he will not offer expiation so that he may do it, then he must offer another expiation. Thus he must offer two expiations.
Ad-Dardeer said in ash-Sharh as-Sagheer (2/217): Or he swears that he will not do such and such, and he swears that he will not break his oath, then he breaks his oath, such as if he says: By Allah I will not speak to Zayd and by Allah I will not break my oath, then he speaks to him. In this case he must offer two expiations: one for breaking his original oath and another for breaking it. End quote.
The expiation is to feed ten poor persons, or clothe them; whoever is not able to do that must fast for three days.
And Allah knows best.