How much should my childs dad pay towards his children every week age 5&7?

me and my kids dad are not together, I only get uc because i have been looking for work but can never find a job were i can work around my kids that i can do just part time in term time. I dont get much help and the kids dad always refuses to help because he would be at work and says he earns more. i get 1,400 a month uc&cb , i pay all the bills rent , ct , water etc internet for our kids& things like netflix , the gas that costs how much when i have to put the heating on , i pay for kickboxing and the busfair & im struggling all the time with the way cost of living is. There dad picks up 800 a week and ontop of that 1,400 a fortnight and then if he wants to do anymore he will book private jobs. he drives around in a Mercedes has a bmw that just sits there , which be should be able to have nice things how hard he works but he has said he's only giving 50 pound a week, there's some weeks he won't even give me any money when i mention going to claim child maintenance he says he can work around that , i dont no if im being unfair for expecting more but when i leave the house with the kids its busfair food, drinks while we out and then paying to actually take them places then when were at home im obviously paying for all the food shops then the heating , buying them little treats etc , even tho he has his own home he knows how much my gas is and that i struggle putting the heating on for kids and everything with the cost lately but if i mention anything it just causes arguments and he makes me feel like i shouldn't be expecting more, his out there doing what he wants buying himself what he wants while im struggling with our children, last week we had argument he diddnt give me any money but then come in to see the kids with a new coat and jeans on while i was literally going without much food etc to provide for my children i find it really hard near Christmas he just always has a way of making me feel like im expecting to much and i shudnt expect more😞

How much should my childs dad pay towards his children every week age 5&7?
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