Where do I stand with the CSA?

Hello just need some advice, I drank beer sowed my seeds has a young lad of 19 dose this girl got pregnant we both didn’t want a child at this stage and I gave he the £200 sorry to say for an abortion and went our separate ways.

I then met my ex who had a 6 month old boy who I brought up has my own and we went on to have another boy 2years later we separated we my eldest was 7 may I add she was playing away from home my eldest told me. 🙁

Since I left I’ve payed her money every week not though csa if I’ve missed one I double up the next week has you do I have them for tea twice a week and every other weekend to stay and give them any thing they need on a regular basis ie clothing extra.

Now my ex is going to csa has she thinks she will be better off than the 35 pound I give weekly, now to top it all of after 14 / 15 years later this girl I gave money to for a abortion may I say I haven’t seen in that time has come back out the wood work and bit me on the bum with am the father to her girl of 14 and she does look like my youngest boy and wants money from me that she owed.

Right how do I stand with the csa I now my eldest isn’t mine biological but he is in my eyes and dosent now that am not.

Do I have to pay for all three witch I don’t mined but will I get back dated for this girl I haven’t met yet just seen a photo of her.