[Joeri]

If you can't leave, you have no leverage and rely on the benevolence of others (a trait which is exceedingly rare). I've been in the situation where I went from being the junior hire to the team lead, with only minor pay adjustments. All it took to fix that was to point out (nicely) that I expected to be paid what I was worth, and they had the choice to do so or to risk me walking out. Line up an alternative, then leverage that into a better situation. If you have no alternative, you're not underpaid, regardless of fairness.

[spoiler]

I could leave, but I am not sure I want to. I like the people and some of them have become my good friends and the job was genuinely fun until I became a donkey.

I have enjoyed most of it, apart from the parts highlighted earlier which frustrate and upset me.

My alternative is to quit and sit at home. One of the reasons (I'm not sure how relevant it actually was) why I took the job was because my doctor said it'd help manage my depression, and it did, because it made me happy, and the atmosphere and coworkers were amazing.

Although, if by alternative you mean another job, I don't know if I'll be able find one close enough so I can still take care of my mum.

Underpaid isn't really the problem, it's just a symptom of this "broken" culture, where anyone new won't ever be as valuable as the new crew (regardless of their actual value or how much they contribute). And I feel part of my problem right now is that that I'm in the department with all the old employees.

[burnallofit]

You do "tech support" and are generally tech savvy? Try getting a job doing remote QA. There are online services for testing apps/software. I work for a company that employs such a service to test our stuff.

Now, your real goal, it sounds like, is not to leave your current job, it is to get paid better. You can't do that without mobility.

[spoiler]

I took the tech support job because it was the only tech-related job.

If I do get to doing work remotely, I'd enjoy development more than TS.