My maternity cover got a promotion

My mat cover (contracted for 12 months) has received a promotion and I found out via LinkedIn and my employer hasn’t contacted me about it 🙃 She’s also removed ‘maternity cover’ from her title so I don’t know if she’s now permanent and when I return if she’ll now be my manager. I’m frustrated and annoyed as I’ve been working towards a promotion and feel like it’s been taken away from me. I also trained her up a month before I went on Mat leave, so it feels like I’ve been blindsided. Are they able to do this and where do I stand? Any advice welcome (I’m based in the UK)