I can provide some general insights into why a narcissistic ex might behave in such a manner.
Narcissistic Injury: Narcissists have fragile self-esteem and a deep fear of being abandoned or rejected. When a relationship ends, it can be a significant blow to their ego. Their response might be an attempt to regain a sense of control and power by lashing out and hurting you emotionally.
Projection: Narcissists often have difficulty acknowledging their own flaws and shortcomings. Instead, they project their negative feelings onto others. By saying hurtful things and blaming you for everything, they are avoiding taking responsibility for their own part in the breakup.
Need for Attention: Narcissists thrive on attention, whether positive or negative. By sending hurtful messages, they are seeking a reaction from you, which can provide them with a sense of importance and superiority.
Emotional Manipulation: Narcissists are skilled manipulators and may use aggressive and hurtful language to keep you emotionally engaged. They might hope that you'll react emotionally, giving them an opportunity to exert control over you once again.
Jealousy: If they see you moving on or being happy without them, it may trigger feelings of jealousy. In response, they may lash out to bring you down emotionally.
Desire to Prove Superiority: Narcissists have a constant need to feel superior to others. Expressing contempt and hatred towards you may be a way for them to reinforce their belief that they are better than you.
Remember, the behavior of a narcissist is not a reflection of your worth or character. It's essential to focus on your own well-being and healing after a toxic relationship. If you find it challenging to cope with the emotional aftermath of this encounter, consider seeking support from friends, family, or a therapist who can help you navigate the healing process.