wrong DNS IP address for dialup clients

[mnisay]

hello.
before, the assigned DNS IP address are being properly assigned to dialup customers, now that
we have changed our IP block addresses, 10% of the dialup customers are still getting the OLD DNS IP
addresses, which is wrong.

i have checked all the routers and servers and did not found any devices  that uses the OLD
IP block nor the old DNS IP addresses.

i have tried restarting routers, clearing DNS caches from DNS servers as well.
i have tried testing different dns attributes like

Client-DNS-Pri / Client-DNS-Pri pairs
Ascend-Client-Primary-DNS / Ascend-Client-Secondary-DNS pairs

i double checked name-servers declaration in the router level , what could it be?

my resources says:
freeradius-0.9.1-1 under FC2

would appreciate advises pls.
thanks in advance.

msn