Incoming call vibration cannot be stopped for silent ringing type (Known Issue)
It is not possible to programmatically stop the incoming call vibration when the ringing type is "Silent" or "Beep once" in the active profile. However, for other ringing types ("Ringing", "Ascending", or "Ring once"), incoming call vibration can be stopped using the [Phone Client Extension API] (available only for S60 3rd Edition, FP1 as an SDK plug-in API) or the Profile Engine Wrapper API CS001294 - Setting the profile tones in active profile using Profile Engine Wrapper API (S60 3rd Ed FP1 and onwards).
This is expected behaviour. No solution available.