Issue with SIM900 Network registration

I have a SIM900 module on which I have a T-Mobile Data Only SIM card (pin unlocked). I am powering on the SIM900 module using a power adapter which can supply voltages 4.5, 5, 6 7,5 and 9 V and 2.1A. However, no matter whatever voltage I select, the SIM900 never gets registered to the network. Please see the below AT commands and response I get. I am a newbie in this, any help will be greatly appreciated.

AT
OK

AT+CSQ
+CSQ: 23,0
OK

AT+COPS=?
+COPS: (1,"T-Mobile ","T-Mobile ",“310260”),(0,1,4),(0,1,2)

AT+COPS
+CME ERROR: operation not allowed

AT+CCID
+CME ERROR: SIM not inserted

AT+CREG?
+CREG: 1,0
OK

AT+CPIN?
+CME ERROR: SIM not inserted

I am following the steps in the arcticle https://lastminuteengineers.com/sim900-gsm-shield-arduino-tutorial/ to connect this SIM900 module to an Arduino Uno and trying out the AT commands using Arduino IDE.

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