My CNC refuses to use my preferred name

So long story short. I recently started a new job. I prefer the shortened version of my name (think like Liz, instead of Elizabeth). This is because of some trauma associated with my name, and hearing the full thing can be quite triggering to my PTSD. Multiple times I have asked to use my preferred name. They say oh sorry, then continue to say my legal name. This has been happening for weeks

I don't feel comfortable explaining why I don't like my legal name as I already feel like shit when working with them and it feels like if they cant resepct a simple name, they wouldnt respect this and or use it againts me. It's getting to a point where it is really affecting my mental health and I don't know what to do. Please help.