SerialPort dialing a number with ATDT command porblem sending ATDT twice

[Dorown]

Hi All,

I am working on a little progrm that dial to a number for example "ATDT9922" this call get to international gate and then I can call International call.
When ever I try to send "ATDT00334542845466" for example the call is disconnected.
I also found that after call is made with the first ATDT command every other AT command that i`ll send to the SerialPort the call will dsiconnect.

I use VS serialPort from the ToolBox and to the following command to send the AT:

//Button 1
serialPort1.Open();
serialPort1.write("ATDT9922" + convert.ToChar(13));
 
//Button 2
serialPort1.write("ATDT00334542845466" + convert.ToChar(13));
 

I press on Button1 and I can make the call and everything is working as expected.
When I press on Button2 the call is droped.
I also tried seding anyother AT command and the call is droped also.

What am I doing wrong here ?
Is there any other way to dial digites after the call is connected ?

Sorry for my english..

Thanks alot!
Doron

[Dorown]

Anyone can help with this issue ?