Is this unusual

Hi, this is the first post I’ve done so bare with me,I went for a smear back in Jan and it came back with abnormal precancerous cells to a high level, so I went to the colposcopy clinic some weeks later the 20th of Feb and when I was examine he said he couldn’t see any cells so didn’t want to do the colposcopy at this time, so he did a core biopsy, which again has come back with high level abnormal cells. I was just wondering if anyone else had had this experience or can maybe explain why he couldn’t see anything if it was high levels ? Thank u for any advice In advance x