South Africa - Ex do not want to pay child support and making life hell!

[Nightchild]

Myself and my ex split up when our children was still very small. I paid child support from the beginning without being told to. They lived with her for 2 years then she sends them to me because she said she could not support them. They lived with me for 3 ½ years then she took them back, three months later she phoned and told me I had to go and pick up my children because she has left them at her ex boyfriend of the times house and they have been there for 2 days, what could I do, it is my children and I love them so I went to fetch them. They lived with me again for 1 ½ years then she took them back again, I have been to court about this, but they said I could not do anything because me and my children’s mother has never been married. They lived with her for 9 months then she send them back again. They have been living with me for 1 year now, in which their mother only phoned them roughly 4 times and never made any attempt to visit them.
My current girlfriend and I have been together for 8 years now and she has been there through everything, we also have a child together and she has raised my girls as if they were her own and for more years then their own mother did, they see her as their real mother because of this and every time my ex takes the children my current girlfriend is hart broken and she and the children always cries over this. My girls are now 9 and 10 years old.
1. The last time that I fetched them my ex signed an agreement between us that she would not take them back again, that she is giving them to me, but it is not a legal document.
2. I always paid child support when they lived with her, but in all the years she has never paid me a cent, even though she always made empty promises that she would.
3. She refuses to go to court because she said the last time when I fetched the children from her that the police was looking for her, something to do with drugs, but she is a compulsive layer and I don’t know if it is true.
What can I do to make sure my girls stay with me where they have a stable future and where I know they are safe, and how can I get her to pay child support, what can I do?

[AFFA]

I wish to inform you that you may have rights towards child under Section 21 of Children’s Act of South Africa. In this regard unmarried fathers right to children have been recognized. You may have paternity proved so that you may exercise your paternal rights in court. If mother intends to take children from you then you can inform her that you have right to kids. Further you may take custody from court. Court considers best interest of child as main consideration.

AFF

Take her to court and/or get Child Support Enforcement involved.