Moved on, ex is in rebound and calls even on diff numbers

My ex left me in August last year, not really any reason as she made up multiple and they changed by the day, but I’m pretty sure even before breakup something fishy went on as she was following more and more guys and getting distant, but she was pretty much instantly in a rebound and still is right now

So on my bday in November she contacted me, message wasn’t even a happy bday, was just all about her, Im too nice unfortunately and replied, tried to be mature and just said hope she’s doing well and gets whatever in life, I blocked after I had no reply for a while

In January she then messages me on a diff number saying she missed me and wants me back, saying she’s been crying and thinking of our relationship and how good I treated her and everything, I respectfully rejected as I have realised I don’t want someone like her in my life, tried having mature convo about life and everything, she then told me to ‘burn in hell’ which I obviously blocked again

Now in march I received a call last week, just random call from her on again a new number ( can tell it was her as it’s WhatsApp, shows the name ) and haven’t heard anything since

This is all while she’s in a rebound relationship with some guy, which after her trying to contact me, I’ve stalked a bit, and she is complaining that he’s not treating her right and he’s messing around with her

So is this rebound relationship just some fake relationship with no real love just to try prove something to me or hurt me or whatever while really she does miss me and regrets her decision but can’t come to face that so is doing all that instead

Why do they do this ( she’s a fearful avoidant or even narcissist if I didn’t mention )