ingrate|ingrates

我们帮了他那么多，他却连句谢谢都不说，真是个忘恩负义的人。

We helped him so much, but he didn't even say thanks - what an ___ingrate!

我帮了他们那么多，他们连句谢谢都没有，真是一群忘恩负义的人。

I helped them so much, but they didn't even show gratitude—such ___ingrates!