So, a quick background...
I started at a company in 2018, and my new colleague, who I'll call X had been there a year already. The role that had been advertised and I had been employed for was taken over by X before I started and so instead I was to replace their role. Shortly after starting the company realised that I was being underutilised and gave me extra responsibilities which upset X, as they wanted me to be their junior and now I was on the same level.
Then, another, higher position became available, which I applied for as had the qualifications and knowledge to undertake that role, but X was unhappy, and I think, dissuaded them from promoting me. A year after, that person (let's call them Z) left the position (I trained them and advised them, despite them being my manager), and so I applied again and was promoted.
Now this has put X's nose out of joint as they keep emailing questions and requests to Y who is now working in a freelance position, but doesn't have the authority, or knowledge to answer the questions. When I asked X why, they said that Y was more qualified than me, even though we are qualified to the same level.
This has been going on for over a year, I've spoken to my manager, but nothing improves.
I've already put in grievances about X as they constantly speak over me in meetings, and their general attitude towards me is awful. Other colleagues have said that they wouldn't stand for it, but what can I do?