Under the New Civil Code, at least 16 year old minor males and at least 14 year old minor females were allowed to marry. Males under 20 and females under 18 were required to get parental consent. At the time, the age of majority was 21, NOT 18.
Your mother's marriage to her first husband in 1980 was valid, barring any other legal impediments.
This means that you cannot be legitimated. Even if the first husband is dead or even if he died after your mother "married" your father, you cannot be legitimated because at the time you were born, your mother had no legal capacity to marry your father (since she was married to someone else at the time).
Your best solution would be for your mother and your father to adopt you so that your status would be raised to legitimate.