Paying zakaat al-fitr in cash is not acceptable according to the majority of scholars, because the Prophet (blessings and peace of Allah be upon him) enjoined that it be given in the form of the local staple food, and it is not known that he or any of his Companions gave it in the form of money.
Al-Nawawi said in al-Majmoo’ (6/113):
It is not acceptable to pay the cash value of zakaat al-fitr in our view. This was also the view of Maalik, Ahmad and Ibn al-Mundhir.
Abu Haneefah said: It is permissible. This was narrated by Ibn al-Mundhir from al-Hasan al-Basri, ‘Umar ibn ‘Abd al-‘Azeez and al-Thawri.
He said: And Ishaaq and Abu Thawr said that it is not acceptable except in case of necessity. End quote.
See: al-Mawsoo'ah al-Fiqhiyyah, 23/343-344.
See also the answer to question no. 22888.
If a person follows the view of the Hanafis, ‘Umar ibn ‘Abd al-‘Azeez and al-Hasan al-Basri, that it is permissible to give the value of zakaat al-fitr in cash, based on the evidence that he regards as more correct, or following the scholars who said that, it is acceptable in sha Allah.
Shaykh Ibn ‘Uthaymeen (may Allah have mercy on him) was asked:
If a person pays zakaat al-fitr in cash, following the opinion of the scholars of his country, then comes to learn the more correct view, what should he do with regard to his charity??
He does not have to do anything. If a person does something on the basis of a fatwa from a scholar or following the scholars of his country, he does not have to do anything. An example of that is if a woman does not pay zakaah on her jewellery and remains for several years not knowing that zakaah is due on jewellery, or on the basis that her scholars have advised her that no zakaah is due on it, then she learns the ruling; she has to pay zakaah after she learns the ruling, but before that she does not have to. End quote.
Liqaa’aat al-Baab al-Maftooh, no. 191, question no. 19
Thus it is clear that if your father pays zakaat al-fitr on your behalf in cash -- based on his following the scholars whose opinion that is -- it is acceptable and valid, and you do not have to do it again in the form of food so long as your father is responsible for spending on you and you are not yet spending on yourself independently.
And Allah knows best.