[Serusers] Sort question regarding INVITE and timeout

Hello, I could not find answer to my question in the list though it was discussed before without ultimate solution :) I have customer who registered on SER then go offline (internet connecting or power problem) Call coming from cisco and going via SER to this customers. I have INVITE from cisco Ser sends trying to cisco Ser send invite to customer Ser send invite to customer Ser send invite to customer Ser send invite to customer Cisco sends cancel to ser... And that is it. And that is not what I want... because falure route supposed to get control over the call and send it to voicemail. I tried playing with timers on cisco/ser but without success. Any ideas? Thank you