When your child turns against you then you should get your child into therapy as soon as possible where they can discuss the beliefs that has turned them against you.
However try not to take the child's behavior toward you personally and instead try to work to build an even stronger trusting and loving relationship with your child so that they feel safe with you.
There are many reasons why a child may turn against or reject a parent and resist spending time with them or refuse to.
This rejection can be a natural consequence of experiences such as parental conflict before or after separation, family violence, personality factors, or poor parenting.
Children can become alienated from a parent for a variety of reasons, such as sexual abuse, physical abuse, emotional abuse, parental abandonment, adult alcoholism, narcissism, and other reasons.
Signs that your child is being turned against you include.
Your child avoids visiting your side of the family; Your child is showing a great deal of anger toward you without reason; Your child always sides with the other parent; Your child does not want to talk about good memories of your times together.
It may be appropriate not to give up on an alienated child but to give space when the child is an adult and has made it clear that they do not want a relationship with the parent.
As children grow up and become adults, they have the right to decide who they want to have in their lives.