Parenting payment question.

Hey everyone,
I'm currently new to these forums and thank you in advance for any help or knowledge.

So my son is currently nearly 3, I've received ftb for the last 6months for him, never received parenting payment as was happy letting his mother get it as didn't want him not having his necessities while he was with her(mind you I've always had him minimum 50-60% of the time.
I recently applied for it and got rejected due to not having proof of receipts and nappies and stuff like that(never once thought of keeping that stuff) and as his mother doesn't wanna lose the payment she won't tell Centrelink I have him at least 50-60% minimum of the time.
What should I do? Any advice would be greatly appreciated.
Thank you