Data Port above ONT box for fibre broadband

Hello,

I recently moved into a new build flat with communal fibre optic router installed. In order to get Internet I had to order a router from internet provider which plugs into the one already installed here.
When first opening the cupboard there was a Ethernet cable plugging into the existing router going to a data port just above it.
The data port has a wire from the back of it going off into the wall.
My new internet only worked when i took the cable out of the data port and plugged it into my new router.
Just wondering if anyone knows what the data port is for and do I need it connected to any where ?

I didn't find the right solution from the internet.
References:
https://www.cnet.com/forums/discussions/data-port-above-ont-box-for-fibr...
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