error while sending AT command for USSD

have been trying to check my credit in sim card by using the at commands but it has not been fruitful. I have been trying to solve this for a while now but nothing is working. Please, i need help.
Below is the list of command and their respective responses:

AT+CMGF=1

OK

AT+CSCS="GSM"

OK

AT+CUSD=1,"*101#",15 (To check credit)

OK

+CME ERROR: 264

Hi, sir

what device do you use? and what do you want to do for USSD?

Hello.
I am using a GSM modem. I just want to check my credit though the GSM.

Hi ,sir

Please confirm whether the operator supports ussd to inquire the credit, and attached you will find the manual of AT command.
and can you give me a photo of "SYSTEM-Information"?

The operator supports the ussd and i can hardly find anything helpful in the manual.

Hi, sir

please try to send "*101#" in your mobile phone dial with same sim card to check.
and can you give me a photo of "SYSTEM-Information"?