Problems with Huawei E173 AT USSD commands on RB435G

Does anyone have experience with the a similar setup? Any RB with USB and Huawei E173 modem?
I can send and receive text messages with AT commands through Terminal, but when I send

AT+CUSD=1,"A3988C3602",15

which should check my account balance, all I get is

OK

. It doesn’t show me the reponse. Is there something I’m missing? I’ve also tried

AT+CUSD=1,"2331323413",15

which is the 7bit equivalent, but the same OK without the response. Can anyone help?