Get off all social media. If you live in a ok country, wear full mask around your head including ears and hair. If not, maybe wear a respirator type as an excuse and if that isn’t viable, move away from urban areas and do not use any technology. If you can’t do any of that, I am really not sure.
Still other forms of tracking though with other geo location services from connecting to WIFI with their phones EMEI being tracked so when other people had connected to that WIFI, they could know where they were and therefore exactly where that WIFI is and track when they connect their device. Also gyroscopes/accelerometers being very developed in phones of today so still being able to track where they were and uploading that information when connected to the internet and then being able to find them again. Technology was made to spy. Do not use technology.
Do you know the identity of that actor? If so, are you prepared to identify here the nature of that actor? e.g. state actor? criminal gang? corporation? personal vendetta?
It is possible that you should have posted this in the registered users only category so that it is not publicly visible. If you wish to do that then you should create a new user and discard this one.
Are you getting a professional to resolve that? It may be quite difficult. What kind of device? Firmware on what device?
Maybe buy a cheap non-smart phone. That will reduce the attack surface for the phone (but obviously if the sophisticated actor is your own government then you should just not use a mobile phone at all).
For your Android and iPhones, the answer is easy. Just do a factory reset. Unless you rooted your phone, nothing on your phone should able to survive a factory reset. If your phone was rooted, you might be out of luck. Doing a deep wipe on a proprietary system (if you can even do it) will probably brick the device if you don’t have the manufacturers secret firmware to restore afterward. If your PC is infected, you needed a Librem PC anyway. Time to get one.
There is a criminal organization in Brazil using NSO Group’s Pegasus to infect devices for hack for hire, to incite terrorism, blackmail people, produce illegal pornography and assist in assassinations. They also have other advanced malware, like UEFI implants and even persistent implants for Kindle and Raspberry Pi.
Brazil won’t do anything to stop them. Only the FBI, CIA and NSA can stop them.
There is also the possibility that they were engaged on the hack of Bezos’ smartphone.
If you know of any security researcher who wants to reverse engineer the exploits they are using, I am more than willing to help them.
If you want a story about how they operate, I am willing to work with you to expose them.