Dtmf tones blocked?

Hello, its possible that the phone company (no voip) blocks my dtmf tones? my problem is this:

I made a system wich calls automatically with asterisk (with a voip provider), then wich was called dial a number (with some options) and it is write in a text file. I have a problem, sometimes when the user dial the option, asterisk doesn’t detect it,so the call is hanged up without write mi text file.

I have change between the diferent modes in dtmfmode, dtmfcompensate and relaxdtmf. Also i have tried changing the voip server and the problem continue.

Please help.

The problem is in Argentina - Cordoba - Rio Cuarto