Have you talked to your manager about your workload, and what did they say? If you haven't talked to your manager, why not?

@PhilipKendall, my manager knows the situation on the project and he would have to be an idiot not to know how much I'm working - he sees me online at 9 pm and 7 am. Still, at my company a lot of people work a lot, although in my case that's currently quite extreme. I'm trying to solve it for now by sticking to my tasks more than I did in the past but also - the topic of this threat - by saying "sorry, but sorry, no" a bit more frequently.

Is starting with not doing unpaid overtime an option? That's never a good idea.

@Erik, I always hear that but then my boss's boss schedules a meeting at 7 pm. What should I do? Or the deliverables are unrealistically scheduled. And most of my colleagues do overtime. I'm dreaming about starting to work as a freelancer to be treated more normally and charge for every hour, but it will still take me some time.

what's your location?

You already tried talking to the person responsible but nothing changed. Now, talk to your project lead and if there is no solution to it then try talking to your manager. One of them will surely have a solution about this and they will act in your fever because from your problem described your upper management will understand that it is reducing the productivity for the company. And no company wants that.

Sounds like the problem is with this one colleague who keeps scheduling meetings. Is that fair, or is it a wider problem? And he's a peer not a manager/PM/superior? If it's one person then you're just going to have to have a conversation with him and explain that you have work to do and there are other people he can bother if he needs stuff (it may well be that everyone else has already politely told him to get lost). If it's a wider corporate problem, then other approaches will be needed.

@J.... You misunderstood. I write that he's my peer, not my manager.

@user216856 Well that's even easier - if you don't report to this person and they're just a co-worker then tell them to get bent and to stop bothering you when you're trying to get your work done. There's no problem here unless you let it become one.

Are you any kind of "lead", "architect", "manager", or anything else along those lines? Or just an ordinary worker?

Is the meeting one-on-one, or did your colleague invite other people to the meeting? As for your boss's boss scheduling a meeting 7 pm: are they in a different time zone? Barring a real good reason, scheduling a meeting at 7 pm is very abusive behavior.

If your team has retrospectives, it could be a good idea to suggest that every meeting include an agenda and expected outcomes. If nothing else, that can help streamline this communication a little.

The freelancer comment is a joke, right? Because you feel like your work atm is even worse than a freelancers. RIGHT?!

Re "working in silos", just tell your co-worker that that's what is necessary to get the job done.

People like going to meetings. The alternative is often to do some actual work. Your pay is the same either way, so no contest!