I'm on a project and have a defined role. A colleague who has been with the company for 15+ years (I've been there for around 6 months) has been regularly doing what I'm assigned to do: communicating the project results and aligning with stakeholders on a specific topic presenting himself as the person responsible.
I've asked him not to many times. I've also asked the stakeholders to treat my communication as the official one, not my colleague's. It works a bit sometimes, then it doesn't. And the discussion has to be conducted again and again.
Above all, I've asked my boss to clarify and communicate the responsibilities. My previous boss jumped in a lot to explain to the colleague and me the role division and intervened in front of the stakeholders when needed.
Then I got a new boss, who doesn't want to take a stance. I'm getting criticized a lot by different people, even in my boss's presence. People claim that I'm not doing my job, that the communication isn't consistent, alignments aren't met. Mine are. But I'm not responsible for what a colleague is doing.
I've asked my bosses to clarify the role division explaining that if I'm not to be responsible that's completely fine, but let's clarify and communicate the responsibilities. They don't want to do that.
We've had a discussion and escalations about that almost every week for months. I feel that my boss doesn't want to lose popularity points with the colleague (who knows a lot of people in the company) by explaining the role division. What's the way to do here? I'm at a point when I fear starting my work every morning because I know I will be attacked for what doesn't depend on me.