Handling nurse manager issue

Hello,
I've searched on this forum and did not find much help. I am dealing with a situation now where the bottom line the nurse manager of last unit has decided (even though to my face said she would give reference) not to give me a reference. I believe that this has cost me a position. Has anyone gone through this that can offer sound advice?

HR is trying to say that nm not giving a reference is not bad but I know and have been told that it gives the impression that I am a problem. Any advice would be greatly appreciated. This whole matter is personal and I am grateful to say that I have had peers that have stated they always let the wrong ones go etc... Thank you for your time.