False answer supervision

m using asterisk 1.4 with a2billing 1.3.2 for calling card operation.Every thing works fine except answer supervision.

It is having 2 nos of FXO 24 port TDM cards one for incoming and other for out going.When incoming call is received agi works perfecting and routes call thru second card to destination,but the problem is even for voice prompt (customer unavailable or switched off also) it is charging the cost and deduction is occured in card balance allocated,this is false answer supervision.

My current a2billing agi-conf1 :

[agi-conf1]

; the debug level
; 0=none, 1=low, 2=normal, 3=all
debug = 0

; Asterisk Version Information
; 1_1,1_2,1_4 By Default it will take 1_2 or higher
asterisk_version = 1_4

; Manage the answer on the call
answer_call = YES

; Play audio - this will disable all stream file but not the Get Data
; for wholesale ensure that the authentication works and than number_try = 1
play_audio = YES

; play the goodbye message when the user has finished.
say_goodbye = NO

; enable the menu to choose the language
; press 1 for English, pulsa 2 para el español, Pressez 3 pour Français
play_menulanguage = NO

; force the use of a language, if you dont want to use it leave the option empty
; Values : ES, EN, FR, etc… (according to the audio you have installed)
force_language =

; Introduction prompt : to specify an additional prompt to play at the beginning of the application
intro_prompt =

Extension.conf :

[a2billing] - incoming
;CallingCard application
exten => s,1,DeadAGI(a2billing.php|1)
exten => s,2,Hangup

[outgoing]
exten => _X.,1,Dial(${RYRM-TRUNK}/${EXTEN})
exten => _X.,2,Hangup()

I Had made changes even in zapata.conf also changing below parameters.

answeronpolarityswitch=yes

callprogress= yes

progzone=yes

Still im having problem of fake billing and false answer supervision. Strucked on same issue for long time,i had made changes according to previous posts in forum,but still same.

Some one pls help me to resolve this issue.Thanks alot