Is it permissible for a woman to marry a boy whom she likes and has talked to for some time as her father did not agree after two times proposal request. Also, the father said it is haram if you marry that guy. Is their marriage valid if they did so?

If the father is refusing the proposal on the basis of Islamic reasons such as the boy does not pray or is an alcoholic then the girl can’t marry without his approval. If his refusal is based on cultural grounds and the girl lives independently in that case she can marry