Downstream frequency not detected - SB8200

Hi, I have bought my modem since August 2023 as a replacement to the modem provided by my ISP. SB8200 never managed to work, and it show the following symptoms :

1. The green light of downstream keep flashing green

2. Startup Procedure

Acquire Downstream Channel : 0 Hz : In Progress
Connectivity State : In Progress : Not Synchronized
Boot State : In Progress : Unknown
Configuration File : In Progress        
Security : Failed : BPI+
DOCSIS Network Access Enabled : Denied

3. Downstream Bonded Channels
Channel ID : 0
Lock Status : Not Locked
Modulation : Other
Frequency : 0 Hz
Power : if the cable is disconnected, it's around -51.6d BmV. When it's connected, the value changed randomly, have values around 0 and sometimes become even positive.
SNR/MER : 0.0 dB
Corrected : 0
Uncorrectables : 0

4. Event log
All the time i have this error
"SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=xx:xx:xx:xx:xx:xx;CMTS-MAC=00:00:00:00:00:00;CM-QOS=1.1;CM-VER=3.1;"

And sometimes this error too
"Lost MDD Timeout;CM-MAC=xx:xx:xx:xx:xx:xx;CMTS-MAC=00:00:00:00:00:00;CM-QOS=1.1;CM-VER=3.1;"

5. I did live troubleshooting with ISP technician. When I plug again ISP modem it work perfectly, so the cable and signal from ISP are working normally. According to ISP technician, the issue is related to SB8200 modem itself, the hardware is defective and is unable to tune in the frequencies.

Can someone please help me and confirm if it's really an issue of the modem itself or if it's an ISP issue? And in case of a hardware failure, how can I be refunded? (I'm still in warrenty period). Thank you in advance for your help.