Burned out in Polish software house

This was my first job in IT, I was a bit desperate when I took it because I am a college dropout. I’m expected to do the SysOps things, CI/CD, backend(Python) and frontend(Vue or React). I’m almost the only person in “the technical team”, there’s only one remote guy that barely helps with C++ stuff. I’m constantly bothered about bugs that were supposed to be fixed by that guy. At the same time clients expects me to be as performant as normal developer. I was living up to their expectations for the first months but nowadays I’m burned out, really really tired. Recently the client requested me to create very complex app, normally project of this size would be created by a team consisting of few people and he thinks that unreadable proof of concept code of the exempt Indian employee is much of a help for me.
After I delievered some code:

I get the impression it would take us many months to finish if you build the whole app yourself

Thank you captain obvious.
I’m being paid equivalent of 850$ per month on B2B after being taxed with some tax exemptions for beginning entrepreneurs. I’m seeing some really ugly attempts of manipulation from my boss - at first I had some appraisals and now he’s been trying to undermine my self esteem so I don’t ask for a raise.
I’ve found out by finding a review on my boss’s company that that the client’s budget has been over 10000$ per month on this project before I replaced the previous employee. He doesn’t help me at all. I am wondering if he had told the client that I’m a junior and charges accordingly less money.
Please avoid Polish software houses if you’re entrepreneur and employ only freelancers, you’ll get much more value for the money and you won’t support exploitation.

@Sebastian - oh my, that does not sound good. Does the client (who said it would take months) understand that large and complex = time? And it must be difficult dealing with a contract person so far away and to hear such huge budge numbers thrown around when you are not getting very much.

What do you think you can do about this situation, if anything?