title: SIM7020E responds on AT+COPS=? with ERROR
body: <p>HW: SIM7020E NB-IoT HAT (from waveshare) + RPI3B + NB-IOT SIM from Vodafone CZ.</p>
  
  <p>I am trying connect to NB-IOT network without success (automatic, manual), AT+COPS command show behavior that I don't understood.</p>
  
  <pre><code>AT
  OK
  
  ATI
  SIM7020E R1752
  
  AT+CGMI
  SIMCOM_Ltd
  
  AT+CGMM
  SIM7020E
  
  AT+GMM
  SIM7020E
  
  AT+CCID
  898823900000********
  
  AT+CPIN?
  +CPIN: READY    
  
  AT+CFUN?
  +CFUN: 1
  
  AT+COPS?
  +COPS: 0
  </code></pre>
  
  <p>Response isn't constant, most common value are listed.</p>
  
  <pre><code>AT+CSQ          
  +CSQ: 15,0      
  +CSQ: 14,6
  +CSQ: 15,0
  +CSQ: 14,7
  +CSQ: 15,7
  +CSQ: 16,0
  
  AT+CMEE=2
  </code></pre>
  
  <p>Until this moment everything seems OK.
  This command in most case end with ERROR +-99% , other time return network list. I don't understood why AT+COPS=? return ERROR.</p>
  
  <pre><code>AT+COPS=?
  +CME ERROR: operation not allowed
  
  AT+COPS=?
  +COPS: (1,"23003","23003","23003",9),(1,"23001","23001","23001",9),,(0-4),(0-2)
  </code></pre>
  
  <p>When I try manually connected to existing, non existing network (AT+COPS=1,2,"23003" AT+COPS=1,2,"23001" AT+COPS=1,2,"23099") with inserted Vodafone SIM card it will stop responding to any command until power cycle.</p>
  
  <p>When I try commands without inserted SIM card  (AT+COPS=? AT+COPS=1,2,"23003" AT+COPS=1,2,"23001" AT+COPS=1,2,"23099") it will respond CME ERROR: SIM failure or CME ERROR: SIM not inserted.</p>