Huh. I don’t have any *good* suggestions, but he’s a hodgepodge of things to check :
You have to use bypass or USB direct to be able to use those commands, transparent/command mode won’t work. Can you get normal responses to other commands? (ie AT – OK; ATI – modem info) Do you have your SIM card installed? The file being cleared is on the SIM card, so it has to be installed. Do you have CFUN set to something other than 0=minimum functionality? At minimum functionality it may not be able to communicate properly with the SIM. Did you try USB direct? With the TH board you can use the side micro USB port for that – keep the USB-c plugged in for power, flip the dip switches by the micro USB both toward the plug, and then use xctu to set device options bit 2 (check the help it might be bit 4 for software usb direct enable) and enable USB direct communication on pin 7 (dio1?).