I am less familiar with simCOM as I am with U-Blox but I think the +CSQ command result is only valid when the device is connected. If the modem is searching, it may return 99 even if there are one or more valid towers with good signal strength nearby.
Try to upload a sketch (like you mentioned you did) where you can send AT commands directly to the module. This is the best way to get started.
Then try the following commands:
report the sim iccid, should match that in the Hologram dashboard:
AT+CCID
response:
+CCID: 89445xxxxxxxxxxxxxx
Verify the simcard is ready
AT+CPIN?
response:
+CPIN: READY
If either of these fail you may have the simcard in incorrectly (sounds like you may not be sure of the correct orientation).
Scan for nearby towers the modem can theoretically connect to:
AT+COPS=?
response:
+COPS: (2,"AT&T","AT&T","310410",2),(1,"T-Mobile","T-Mobile","310260",2),(1,"T-Mobile","T-Mobile","310260",0),,(0-6),(0-2)
This command may error at first, if you get an ERROR or empty response, just leave everything as is for 10 minutes then try it again. Also checkout Nova R410 (Cat-M) Issues (Troubleshooting tips and tricks and known issues on the R410 Nova + user feedback on issues) - #9 by AndrewGifft . I know you are using a different modem but both are Cat-M1/NB-IOT modules so may have similar behavior.
I cant quite tell from your description but also make sure ONLY the cellular shield is plugged in to the arduino. Don’t double-stack shields while debugging (and be careful doing it anyway many are not compatible stacked).
Good luck.