Urgent Help!!

[Sasha2]

I thought perhaps some subspecies of ground snake until I saw your in Paraquay.
If that is a full grown snake for that species I doubt it will acclimate to captivity.
The older the snake the harder it is and since we dont know the species we have to assume its full grown, so best to let it go somewhere safe.

You will have to just keep trying different things, perhaps slugs or even small fish?
Perhaps there is a reptile club near where you live that might know how to care for it. But if no one can identify the species then you need to let it go.