I have the same situation almost. We have fiber from Telia delivered to the basement of our apartment building where it’s converted to cable by Tele2, who rents access to Telia’s fiber. Neither of them were willing to sell me or the organisation that owns the building access to fiber, even though it would have required only activating an outlet on whatever fiber switch thing they have in the basement.
Tele2 also has a monopoly on internet access; it’s that or 4G/5G.
This led to the absurd situation where we have a special coax outlet, followed by a cable modem right next to the fiber switch to supply the intercom system with very very expensive and terribly slow internet.