I recently applied for a job at my current place of work. It's a grade above me and since the previous job holder left I've been doing that role without any extra pay until they could find a replacement. I applied for the job but unfortunately I wasn't successful, despite doing the role currently alongside my actual role. Apparently they know I can do the job well as I'm already doing it, but someone else (without experience) got the job instead as they gave better examples in the interview.
Until the new joiner starts in a month or so, I'm expected to continue to do this role (none of the duties are in my job description) without extra pay. I'm then expected to train the new starter to do a job that I'm apparently not qualified for.
Does anyone know if I can be fired/disciplined for refusing to do this?