Is my definitive severing of relations with my father, in whose care I was raised, considered an act of disobedience (ʿuqūq), knowing that I am an illegitimate child?

If the father conceived you through zina (fornication/adultery), then he is not your father, and he is not entitled to the rights of fatherhood from you. You do not inherit from him, nor does he inherit from you. As for your true mother who bore you through zina, she is your mother, and she has the right to obedience and good treatment from you. Those who raised and cared for you have a great right over you. If the woman with whom you lived was truly your maternal aunt or breastfed you, then she is your maternal aunt or your mother through rada’ah (nursing), and her husband might be your father through rada’ah. Otherwise, it is not permissible for you to be alone with her or to look at her after puberty.