I’m not entirely sure if I understand the question, could you perhaps elaborate?

The Telfort connection you’re referring to, is this a physical connection (DSL/FTTH)? If so then this connection could be changed to KPN by ordering a connection with KPN (Telfort uses the same physical connection as KPN, so if 1 already works then the other should be able to take it over).

You could try entering your adress into fourstack (link below) to see which option's are available according to KPN registration. It's possible that the physical connection will be finished/brought into you're home if you order a physical connection.

Fourstack: https://kpn-compleet-fpi-info.fourstack.nl/

personal disclaimer: since Telfort is becoming KPN, I'm not sure if there’s any restriction's with changing packages and if promotional option's apply.

Hey Zeonz.

I will write more precisely.

 I currently have a mobile subscription in Telfort and I would like to additionally launch home internet because I am interested in the Internet package with smart tv from KPN.  I checked the possibility of connecting by address and it is Ok, but I do not have a cable physically in the apartment, but it is outside the building.  

Details of offer.

https://shop.kpn.com/internet-tv/internet-tv/?telfort=true

Hi Marcin, welcome here. 

If the postal code and housenummer check on our website is ok, you should be able to place an order. After that you can order an engineer to find out where then entrance point of the cable is. There should be one, otherwise you wouldn't be able to place an order. Worst case scenario is that old residents removed the cable entirely, that seems far fetched tho. 

Hi Alex

 Thank you for your answer.  I entered the address correctly, I received the modem on Saturday, now I need to arrange the installation with the installer.  I learned that the cable is behind the wall of my apartment.  

Thank you for your help.

No problem, glad to help. Let me know if I can assist in any way. :)