Can't change SN on EG8145B7N-50

Hello guys! I’m trying to change the serial number (SN) on my Huawei EG8145B7N-50 ONT, but without success. Could someone help me?

Serial numbers by design are not supposed to change. Does the serial number on the belly label not match the serial of the device?

I want to switch so I can authenticate with GPON; I want to get rid of my ISP's ONT.

Which ISP do you work for?

I don’t work for any ISP, I’m an end user.