DTMF input is not complete

Hello. I’m using AsteriskNow registered to a voip provider. The process is simple, I call the mobile phone and when it answers, it will play a voice telling that you need to enter 4 digit numbers. However, there are times that when I enter 4 digit numbers, it is not complete. For example, I entered 1234, on my AgiScript, it will display 134 only. Any idea why this is happening? Is it on my bandwidth?