Hello.
Phone doesn't respond on Software CMDs sent via Modem port. At first, please re-install
Samsung USB drivers, then try to process the phone again. Try to use different USB ports of PC motherboard for connection of the phone.
If problem will remain the same - most likely phone has firmware with new type of Security. In such case You can try to write older (by release date) firmware, or only its modem, then repeat "Repair IMEI" operation.