Advice needed on the CSA

Hi all, can anyone give me some advice please?

I have just received the 1st form from the csa regarding dna testing. Still cant believe my ex has contacted them….we had a relationship and had a daughter 15 years ago. She never wanted me on the birth certificate and we split up after 3 months of my daughter being born.

We came to a arrangement and I paid every month for the past 15 years and my daughter stayed with me on the weekends untill October last year where my ex and I had a massive fallout and I started giving the money to my daughter direct on the weekends rather then the x or her husband.

I have asked the csa for a dna test as I am not 100% if im the dad, my question is this?? I am self employed sole trader and say the CSA has got a grip on me would it be better going to a ltd company so i can pay myself a smaller wage as no way can i afford 15% of my net income? Any advice?