Sorry, you got what you paid for. Kiwi is (IMO) one of the worst online travel agencies and one of the very few that sell "self connecting" tickets, which are highly inadvisable. There are plenty of online reviews to back this up.
They clearly state in their terms and conditions (which you agreed to at booking) that any irregularity is your problem and not theirs.
Multi-city: means a form of carriage which includes a combination of Flights which pass through one or more interim destination(s), which You have expressly selected within the Booking. Please note that in the event that You have selected one or more interim destination(s) where You will spend less than 24 hours before continuing Your journey, We cannot guarantee that the respective Selected Carrier(s) do not make any changes, or cancellations, to the Flight(s) within Your travel to and/or from this interim destination as listed in Your original itinerary; in which case We are not responsible for any financial or other obligations to You or the Selected Carriers in this regard.
Even if you have bought the so-called Kiwi Guarantee, it wouldn't help much in your case. The terms are full of loop holes, restrictions and exclusions. See https://www.kiwi.com/us/pages/content/legal#ContentLegal-article5
What should I do? How could I handle these crooks?
Not much, I'm afraid. You chose to deal with crooks and accepted their terms. Nothing they do is outright illegal. If it's too good to be true, it's often not true.