Please could you add a comment to your original question with the exact AT command response you are receiving?
If AT+COPS=? returns a list containing no network names, this indicates that no networks were found during the scan.
If the module is able to detect networks a typical result will look similar to:
Note that the module will perform the scan in response to AT+COPS=? even if no SIM is inserted, so the SIM card can be ruled out as a potential factor.