send USSD code to D-link GSM modem

Question

I have a D-Link DWM-157 GSM Modem. It is connected to a USB port and it seems working. I can use minicom and miniterm.py to set the right port (i.e. /dev/ttyUSB0) and can get OK for AT and ATZ commands. The problem is that I don't get any response when I run USSD codes. The following is the output of miniterm.py:

--- Available ports:
---  1: /dev/ttyUSB0         'D-Link DWM-157'
---  2: /dev/ttyUSB1         'D-Link DWM-157'
---  3: /dev/ttyUSB2         'D-Link DWM-157'
---  4: /dev/ttyUSB3         'D-Link DWM-157'
--- Enter port index or full name: 1
--- Miniterm on /dev/ttyUSB0  9600,8,N,1 ---
--- Quit: Ctrl+] | Menu: Ctrl+T | Help: Ctrl+T followed by Ctrl+H ---
AT

OK
ATZ

OK
AT+CUSD=1,"*140*11#"

OK

and then no response! Any help is appreciated.