Change Rings Before Voicemail On Iphone IPhone Only Ringing For Five To Ten Seconds Before Going To Voicemail?

IPhone only ringing for five to ten seconds before going to voicemail? - change rings before voicemail on iphone

My phone rings only for five to ten seconds before the answering machine. I have not changed the settings for it and do not understand why you do this, ... If any of you know why, please, please, help me!