CSA leaves me with nothing while ex gets the world on a plate

I’ve had bad doings with the csa in the past they keep saying I owe them £1000s of pounds in arrears witch I still think there wrong I don’t know how they work it al out they say it’s off your income before tax and insurance witch I think is wrong coz everyone as to pay tax insurance i need help with all this coz if you come out of work and you AV no chose you AV to go on to jsa when you get back into a job they sting you saying you £1000s of pounds inarears and you can’t get out of it my ex wouldn’t let me see my kids but I still pay for them and the other thing is that the money Gos to her and not my kids the csa told me that it’s down to her wot she spends the money on when it should be going on my kids not her and it’s ok for her to AV money coming in from every where and being married and AV a morgage and going to university acing five kids to three different people and getting benefit as well as my money I think it’s a joke the way it works she as everything and I AV nothing.