What a sad story! Here is how you could write that:
I was trying to save a puppy. An animal organization was telling me to let him die. This puppy had no home so the veterinarian I took him to did not give the dog a lot of attention. The puppy is now dead.
The puppy was struggling to live and no veterinarian or organization tried to save him. How long will this continue? Why are the hearts of humans so cold?