PPPoE doesn't connect after updating router's firmware

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Router model: Netis-DL4323
I attempted to update the firmware to the latest version (2020), since the current version running is from 2014.
It connects normally to Ogero/central (WAN), but the account (pppoe) doesn't connect at all. I checked the details of the account and its still the same as the old firmware (same values, nothing new added), so I ended up reverting back to the original firmware (2014) to fix it.
Any idea what's going on?

Firmware list: https://www.netis-systems.com/Suppory/de_details/id/1/de/75.html

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Update: I tried restoring the router to default settings on the old firmware to make sure the account details are correct which it was and it connected without issues. Meanwhile, on the new firmware, I tried restoring to default settings and doing the same steps, but the account doesn't connect at all; checking the logs it says: ppp1: link established then ppp1: link terminated. immediately.

What could stop the account from connecting? I tried all firmware they all have the same issue... except the first one released.