How do I change my power of attorney while living abroad?

I’m an American citizen living in South America with my significant other. My mother has always been my healthcare proxy and POA because she was my next of kin and also as a RN, I respected her medical expertise and knew she would always do what was in my best interest if I were to die or become incapacitated.

Five months ago, my mother passed away somewhat unexpectedly at a young age. I left the country shortly after and decided to cut ties with my abusive father after his disgusting behavior finally became too much to bear.

I’ve been thinking lately that if anything were to happen to me, that guardianship would be automatically granted to him as my surviving parent. I absolutely DO NOT want this and want to appoint my boyfriend as my healthcare proxy and have him be my joint POA with my older brother.

I’ve tried calling my healthcare provider but they never returned my calls or emails and I’m frustrated because this is somewhat important to me and would hate for my awful father to have the satisfaction of keeping me plugged into machines or dumping my cremains down the toilet if something happened to me…I seriously wouldn’t put it past him.

What’s the best way for me to take care of this? Can I type something up, sign it and have it notarized? Would it have to be notarized in the US?