I think the command you want is without the question mark...
AT+CCID
Seemed to work OK on my SIM7600.
A T + C C I D CRCRLF+ C C I D : 8 9 6 4 0 1 2 0 1 1 1 0 9 0 9 9 1 5 2 CRLFCRLFO K CRLF
41542B434349440D0D0A2B434349443A20383936343031323031313130393039393135320D0A0D0A4F4B0D0A