unfortunately without his help, there is not much you can do. You have to proof that he is your father and was a U.S. citizen at the time of your mother pregnancy. If he was not a U.S. citizen at that time, you need his help to proof that he is your father and to file an immediate family petition for you.
Elkhalil Law Firm, LLC
Disclaimer: This answer is for informational and educational use only. This answer does not create attorney-client relationship. For more details, I recommend a private consultation with an immigration lawyer.
If he was not a citizen at the time you were born, then he cannot transmit citizenship to you. He could, in theory, try to petition for you, but you would have to show that you were legitimated before age 18. From what you're saying it doesn't sound like that happened. Without his cooperation, proving legitimation and having a petition approved would be impossible.
The information provided is given for general purposes only. It is not meant to provide any specific guidance or give any legal advice. It is recommended that you bring your specific situation to a licensed attorney for a more complete and thorough evaluation.
Ultimately, if your father gained his citizenship after your birth, the only way that you may gain citizenship at this point, would be if your father were to file a petition on your behalf, based on your being a son or daughter of US Citizen. Factors to consider include: your age at time of filing petition; whether you are married or unmarried; but please understand, you can not force your father to file a petition for you. From your statement, it appears that you and your father have little or no contact; so unless he has a change of heart, or you both can repair your familial issues; it doesn't seem likely that your father will file a petition on your behalf.
This response in no way establishes attorney/client privilege or relationship.