I need financial help but my ex refuses

I have two children one aged 10 and another aged 6. Me and their father sepperated around 2year ago and I have never recieved and support financially from him this whole time. He refuses to pay anything if I’m not in a relationship with him.

I’m currently working part time as a special needs support assistant and I struggle to support my children on my own. My children’s father is living at his mothers, he says he isn’t working but many times I have seen him doing gardening work for cash as he used to be a self employed landscape gardener.

I’m hoping you can give me some advice as I don’t know what else to do. He has access to the children his mother picks them up on a Sunday morning and drops them off at tea time he sees them for a couple of hours in this time he doesn’t buy them any clothes shoes or food or any thing.

Yours faithfully

S.Clough