Redirect public client ip

Hello,
This is my network: my clients can connect after pppoe authentication, then they receive a public ip.
All network is routed by OSPF, and for user and password, profile, pool of public ip, etc. there is freeradius + mysql with innoDB engine.
I’d like to use payment reminder, dst-nat + proxy, but it doesn’t work.
What is the right method in this scenario? Thank you.