Good day readers. I need advice on something that i witnessed today.

Ok, I decided to go with my mother to inspect an ongoing project (normal family house) at ishieri,Lagos.
I have been hearing a lot of stories about these rogues but today witnessed it with own eyes.

While watching the labourers carry out their duties, a group of young, hungry and fierce looking men stormed the site and demanded they stopped work ,and my mother asked why, they said we haven't settled them. We were both confused because I believed we'd settled every necessary thing needed to be settled.

A heated argument started and I told my mother to calm her self. Then we told them we've settled everything and they told us that's the "old government". I later discovered that the old people we settled have been overthrown. So we decided to go see their boss, and after waiting for hours while work was still paused at the site, the boss finally came to attend to us and then we explained what his boys did and he told us to pay N350,000 , after pleading seriously with him, we finally settled for N100,000.
That was how my mother parted with N100,000 that was meant to be used to buy bags of cement, sand and settle the labourers on site.

I was very pissed and kept cursing them under my breath. I told my mother to call police or sue them. She then told me how a man abandoned his land for same reason because they threatened to kill him if he steps into that place again.

A woman who didn't pay early enough, her land was sold to another person despite fencing and laying foundation, and from the dispute she was told to pay additional N700,000 to secure the land{land she had already paid for initially}.

Heading back home my mother told me she and my father have spent over N400,000 because of these guys.

Meanwhile, a relative building his house in another state never experienced such.

I thought Lagos state government laid a ban on these thieves.
What appropriate measures can be taken, please? Because from what I heard, the 100k settlement will be just for few months then we would be forced to pay again.