Hello @Baziz 

Did you receive a confirmation that your subscription is terminated?

You can send the modem and poweradapter in any suitable box to the following address:

KPN
Antwoordnummer 10119
2400VB Alphen aan den Rijn

You can give the box off at any PostNL point, make sure you keep the receipt for a couple of months.

Yes I switched to a different provider and they handled the transfer. KPN sent me a message that they will send a box for returning the equipment but I did not receive anything since then. But thank you I will send it to the address that you provided.