Hello, friend!
I'm sorry I didn't solve your problem before, but I'm glad to answer it again.
The forum is mainly for enterprise network products. Therefore, I replied to the forum based on the enterprise network product configuration.
As for your requirements, I have obtained confirmation from the carrier's product technical support personnel that the WAN configuration of the HG8447 cannot be modified by myself.
The reason is that the HG8447 is customized by the carrier. That is, the HG8447 is restricted according to the requirements of the carrier. Therefore, we cannot provide meaningful help to the HG8447.
In the end, I'm sorry to tell you that you can only get a solution from the ISP.
You are very welcome to join the forum, the forum on the product knowledge will help you.
Thanks!