I just returned from about two year break, someone in game told me iron maiden can't be casted by monsters anymore. I think I am being trolled, can anyone tell me if its true or false?

It is true.
The monsters do no longer cast the iron maiden curse.

Specifically the oblivion knights. 1.13 changed that. They also can't cast lower resist anymore.

This is true.

Back in 1.12 Knights in chaos could cast IM and could destroy melee characters.

1.13 took that away.