Whom did Amos call "cows of Bashan"?

Answer: Women of Samaria

Amos rebuked the "cows of Bashan on Mount Samaria", women who oppressed the poor and told their husbands to bring more drink.

“Hear this word, you cows of Bashan on Mount Samaria, you women who oppress the poor and crush the needy, who say to your husbands, “Bring us more to drink.””— Amos 4:1 (BSB)