Other forms: took up the cudgels; taking up the cudgels
To take up the cudgels is to defend or fight for something or someone. If you were scammed, you'd be grateful for an advocacy group to take up the cudgels on behalf of you and the other victims.
A cudgel is a short, thick stick used as a weapon, much like a club. Here, take up means "pick up," so the phrase literally means "pick up weapons." To take up the cudgels sounds very violent, but people usually use this phrase metaphorically. It means to figuratively fight for someone or something by vigorously championing or defending an idea or cause — but usually through argument and debate, not by using actual sticks!