If you run the following AT command, what does it show? AT+QGMR
Mine shows: RM520NGLAAR03A03M4G_01.201.01.201
You may also want to try this solution: GL-X3000 with data only T-Mobile SIM not registering - #4 by ywp
It sounds like it could also be an IMEI issue. Are you using the default IMEI # of the router? Is there a way to test the SIM card in a phone?