I've been on a similar situation once, this is what I did, and I think you're on the right path.
> I tried contacting every retailer.
Try to reach out to the ombudsman (ouvidoria) and explain your case. Even if they don't actually solve the problem, you documented that you tried to friendly resolve the issue.
> I am expecting fallout from this.
Very worst case scenario, the retailers will send the fraudulent invoices to collection agencies and might report you to the credit bureaus. Don't ever pay any cent toward this fraudulent debt. Don't negotiate. The only option is the debt going away as it is fraudulent. It's their money that's on the hook and paying it shifts the responsibilities to you.
Once it hits the credit bureaus, as you already have a Boletim de Ocorrência, and proof of contacting the companies (protocol numbers + dates), i.e. documentation, sue them and ask for damages. It's a simple and common suit that both the credit bureaus and the retailers will want to settle. Make them pay for your time. They don't have any proof that it was your person that made those transactions.
> I am utterly powerless in protecting my identity.
Yeah, but the thing is, if the retailers, banks, credit cards, etc. really wanted to avoid fraud, every purchase/subscription would require the same level of protection as a real estate transaction. Everything signed, in-person meetings, upfront payments, banks, lawyers, notaries, cryptographic signatures (hey, we have e-CPF and nobody uses it!). But as you see, 100% fraud avoidance means friction, and no sane retail business likes friction. It's a business decision on their end. They accept risk so they can take your money easier.