You have write-only database. You need to add code to read back what you have stored and to act on that.

call transfer or call forwarding in asterisk [test] exten => 1000,1,Dial(SIP/User1) exten => 1000,n,Hangup() exten => 2000,1,Dial(SIP/User2) exten => 2000,n,Hangup() exten => 3000,1,Dial(SIP/User3) exten => 3000,n,Hangup() ;call forwarding exten => _*21*X.,1,NoCDR exten => _*21*X.,2,Set(DB(CFIM/${CALLERID(NUM)}=${EXTEN:4}) exten => _*21*X.,3,Playback(vm-saved) exten => _*21*X.,4,Hangup()