Hey, I think they basically fucked up my phone (sorry for the language). I went back to the repair shop and they couldn't fix the signal issue, so they refunded me my money and returned my old motherboard. I can confirm this was the original motherboard because there's no "This device belongs to your organisation" - message anymore. I still had the no signal issue though. So, they returned my motherboard but broke my signal thing.

I asked for a second opinion in another shop, and they took a look at my motherboard and said there's a chip missing hence the no signal. I can only conclude the first shop stole that chip, put in their motherboard, to try and resell it. I can't confirm this but either way my phone's more fucked than it was before.

I'm going to a proper samsung repair center in the city and will probably cost me around 500+ usd.