Blocked call still coming

Hi, I blocked a former friend but the call still comes through as No Caller ID on iPhone. I’m so frustrated because of this. They called many times in one go and it would ring 3 times but then the call would end on its own. If it’s blocked it should go to voicemail straightaway. However this looks terrible on my part as if I’m hanging up every time even though that’s not the case. And this person is able to leave voicemail messages,

please help with this issue. And my network provider won’t block any numbers so I can’t do anything about that.