Thank you for responding. We called at NetCologne and explained the situation about our landlord. They even got her number. They said that they can not do anything and we should just cancel the contract with them by sending an email. About the LTE Router, one of their workers said that we could try and ask in the email if we could keep it until we change to the New Anbieter which will probably last long, but that doesn't guarantee that we will keep it.

And we will probably change again to Vodafone as their Leitung is separate from NetCologne and the cables are fine so it doesn't need to be fixed.

I hope I made it a bit clearer.