What can I do with an IMEI? I want to take revenge

I think this is the correct board for asking these things, but if it's not, my bad. Well, a brief history: I was walking with some friends and I was robbed by 5 guys. They took my phone. I tried to contact my phone company to have my phone blocked, but it was not very effective, they only blocked the SIM card. To do the complete block, I have to go in person to a branch of the company and show some documents... you know, bureaucracy (the thing is that I don't even know if I have everything they are asking for). I could look in the respective documents and all that, but what if I can do something else? I have the box of the mobile, where the IMEI and other info is listed, I even have my phone number (but it's probably pretty useless to have it since the SIM block). So, could I do something “interesting” with an IMEI?

You could have just reported it to the police because they can have access to tracking the phone with the IMEI. If you dont want to go to police before finding out who it is only other method is contacting the manufacturer directly which all they will do is disable the phone if they can distribute this info to cell service companies. Other than that I have no idea if sites like this are legitimate https://imei-tracker.com/

You can demod area signals and drive around asking the femtos if it's connected recently, which is also how the FCC will find you for doing just that.