KPN Box 12 Lan2, Lan3 and Lan4 do NOT work

To whom it may concern,

First of all, I am sorry that I do not write this in Dutch, but I do not have enough knowledge of the language to ask these kind of questions. I will do my best to achieve it in the future!

As the title suggests, I have problems connecting via ethernet to the LAN ports 2, 3 and 4 on the KPN Box 12. I got my internet connection in the house on 26th of September 2023, and the KPN Box 12 a bit earlier in 7th of August 2023. The internet connection is 1Gbit fiber optic. The Wi-Fi works just fine, on any device, as well as the LAN port 1.

I have tried the following:

• Plugging in different cables of different categories: Cat5, Cat6 and Cat6A both crimped by myself and store bought ones. ALL the cables I tried worked on LAN 1 but not on LAN 2, 3 and 4.
• I have tried shutting down the modem, waiting for a few minutes and turning it back on. After doing this soft reset, the ports 2,3 and 4 would briefly work , but very soon the connection would drop, unwilling to come back on, until a new soft restart.
• I  have tried several hard resets, but the ports would work again for a brief 1-2 minutes, only to drop again until a new soft or hard reset.

I fear that the modem has some hardware fault, but in any case, I would like to know if I did something wrong and if someone more knowledgeable than myself can suggest some other thing I could do.

Thank you!
Best regards,

Saila Mihnea