One more long-shot idea that occurred to me, and might be worth your time (totally up to you!) would be to contact your various "scopes" of government. I know next to nothing about Brazil, so I don't know what that would look like for you, but if it were in a mid-sized US metro area I'd look at:
- City Council Representative
- State Department of Transportation or Public Safety (In my case this would be Texas DPS)
- County level law enforcement, not city; (so not El Paso, TX police dept. in my case but El Paso County Sherrif)
- State level law enforcement (Not Texas Rangers in this case, as I think that's for other stuff, but something adjacent if it exists? Just my guess as to an example, may not have even a remote analogue in Brazil)
- Federal law enforcement (FBI in the US for example; filing a report/complaint won't get them mad at you unless you really abuse the hell out of it)
- Mayor's office for your city
- Metro transit authority if you have one
- State House of Representatives and/or Senate (your legislative representatives, if you have those)
- National House and/or Senate representatives (I'm in El Paso, TX so in my case Veronica Escobar - House - Ted Cruz (*shudder*) and John Cornyn in the Senate)
- Federal Trade Commission (oversees trade issues, privacy in the US)
- State Attorney General's office (Texas AG in this case)
- Maybe the equivalent of your state governor if appropriate/possible (for example in my case, Gregg Abbott)
- Consumer Financial Protection Bureau (in the US this is a federal agency, but no idea what the equivalent would be elsewhere or if you even have one)
- Federal Communications Commission (The FCC overseas telecommunications systems and law in the US; equivalent may or may not even exist)
Now you're probably thinking "most of those don't deal with criminal exploitation/violent crime/theft!" and you're right. The goal is to make enough noise about it in hopes that somebody in some agency somewhere will just give a damn and hopefully at least make a phone call to a buddy who knows the CEO or something, or draft a letter, or just do something, nearly anything, to poke Uber in the ribs and give 'em a little pain. Sometimes all you need is the attention of just one person in the right position to get others on board, so more complaints = higher probability somebody will do something.
In the US there's an organization called the "Better Business Bureau", or the "BBB", that maintains ratings of merchants and small/mid-sized businesses and tries to mediate disputes. I don't know much about them or if that would be appropriate in this case if it were in the US, but see if an equivalent exists in Brazil or just your local area. You might be surprised at what you find.
Another possibility: take your story to local taxi drivers/companies that COMPETE with Uber. They might be willing to put advertising dollars behind your story to help create a sense of distrust among the public, getting them a bit "scared" to use Uber so that folks use them instead. A slimy tactic, sure, but if your government won't protect you and your fellow citizens, the "slimeball" factor rests on their shoulders, not yours, because they forced you into a corner by not doing the most fundamental job of any government: providing basic safety by enforcing the law.
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You could also, as others have mentioned, try getting the local (or maybe even national) news media to do a story on this too. Just be aware that being in the public spotlight like that might not be the safest thing for you - retaliation from whomever is doing the extorting could be a serious concern or risk. I doubt Uber themselves would bother you, even through a "proxy" or hired/other "agent", especially as far away as Brazil, so I wouldn't worry about them. The individuals using Uber to harm people, however, might be organized in some way, and they might target you for...something. I don't know what. Don't let that scare you off right away, and don't go buying every gun/weapon you can find "just in case" either, at least not until you're fairly sure you MUST have one. Avoid extreme actions without justified necessity. Don't let this risk put you off entirely - that's exactly why intimidation and retaliation tactics exist and it's the ONLY way they work! Just be aware that there could be some risk depending on your society, laws, public exposure, etc. and discuss that with the journalists involved to find out how to maintain credibility without making yourself an easy target. They might have some pretty clever ideas, so give them a chance!
You're in a tough spot but I appreciate you shining the light of day on this. And you're right, if they don't fix this somebody's going to get mugged, raped, or worse, and it's very likely happened already, and all the while Uber's content to just keep their head in the sand. Not great for "optics" and "public opinion", after all.
I continue to wish you luck! Here's hoping something breaks loose!