Can I re-use old KPN connection in Meterkast?

I have a router with a fiber connection in my living room, it works fine. I need to get wifi in my Meterkast outside the apartment (I am measuring electricity/water consumption). Wifi extender barely reaches it. I was wondering if it’s possible to connect to the old KPN connection (where DSL used to come from) to get internet? Powerline adapter won’t work because electric outlet in Meterkast is on a different electric circuit than my living room. Mesh networks are very expensive