How can my previous employer KNOWINGLY gave false references and have "qualified privilege"?

Regarding "qualified privilege", if an employer knowingly makes false statements, in direct contradiction to statements made in writing and in my HR Personnel file to potential employers, does that negate the privilege, or does that give them a defense? I am a teacher who had a contract last year. I went through the review process with my supervisor. At the end of the year, I had a GLOWING review and ended up scoring higher that what was required of first year teachers. I received nearly all positive comments, with a few "you need to improve in this area" comments. With this information, I used my supervisor as a reference for all my applications for potential jobs between May and October. However, I was unable to secure a teaching position. I interviewed for 3 positions that were perfect for me, 2 of which (subtly) indicated the interviews were merely a formality. However, at the end of the week, I received the "we regret to inform you..." message from all 3 employers. In October, I received a letter from my previous district's HR department stating that I was blocked from substituting at the high school I worked at last year "due to my performance as a substitute last year". I was not a substitute...I was a contracted teacher. Long story short, my supervisor had written an email to the substitute coordinator at that district, along with another teacher (the teacher that was out on medical leave...I taught her class while she was out), and told the coordinator things about me that were in direct contradiction to the glowing review I received in May.

So, I have what my supervisor said about me and my character in writing. It was seen by another person. It is defamatory. It has hurt my reputation. I believe it has prevented me from obtaining a job. However, I cannot prove my supervisor has given false information in references. Is this situation one that may qualify as a Defamation of Character suit? Or does my supervisor still have "qualified privilege" because of the "reference" portion?