Luca
I have looked at the config that you posted and I believe that I see an issue. You have configured accounting for DIALER with this method list:
aaa accounting network DIALER start-stop group radius
I would expect to see the method list DIALER accounting referenced under interfaces Serial1/0:15, interface Virtual-Template1, and interface Group-Async10. I suggest that you add:
ppp accounting DIALER
under these interfaces and let us know if it helps.
HTH
Rick
HTH
Rick