Why is this happening? Why is my ex's girlfriend trying to contact me?

THIS IS THE 3RD DAY IN A ROW NOW. I am getting annoyed! This new girlfriend is also his ex. He went back and forth between me and her for 2 years. I have her number blocked. I also have restricted calls blocked. 2 days ago she called me off her number, then restricted and then some number from an app. AGAIN, today, 3 times, she called me off of the app number even though it is blocked. What is the reasoning behind this? We don't like each other and the guy is a douche. I don't understand. I do not want to talk to her.
Why is this happening? Why is my ex's girlfriend trying to contact me?
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