Is it obligatory to change the surname and announce the adoption, and is the paternal uncle considered among the kin whom one must maintain ties with despite his harm, especially since adoption makes him not a true relative?

An individual of unknown lineage is a victim of weak religious and moral deterrents, and they must endure with patience and entrust their matter to Allah. Adoption is forbidden by Sharia, as Allah Almighty says: "Call them by [the names of] their fathers; it is more just in the sight of Allah." Therefore, you must change your name in official documents if it carries the lineage of your caregiver. If changing it is not possible, you must agree with the family on the true situation: that this lineage does not imply the impermissibility of marrying their women or entitlement to inheritance. You are not required to publicize this to everyone, and there is no sin upon you regarding the lineage that has become known, but strive to amend it officially and refer to yourself by another name when introducing yourself. It is permissible to address the family with respectful titles as a figure of speech, not as a statement of actual lineage. The rights of righteousness and kindness are not exclusive to parents; they include anyone who has shown you kindness. There is no harm in avoiding mixing with those who cause problems, while repelling evil with good. In summary, it is not permissible for you to intentionally attribute yourself to the family, and there is no sin upon you if your lineage became known unintentionally or if changing the documents is impossible. You are not required to verbally disavow everyone who calls you, but do not introduce yourself by attributing yourself to those who adopted you.