Hello @Senator Frank ,

When the sim card is locked, you need a so called Pukcode to lunlock your phone. You can get the code online: https://www.kpn.com/service/mobiel/pukcode.htm. 

After nine months, you are too late en then you lost the number forever.  

Thanks for the answer! My SIM card is active, sees the network, but I cannot pay for it online. When trying to pay via the link https://www.kpn.com/prepaid/opwaarderen.htm, the phone number field says that the SIM card is not active. You can write me detailed instructions on how to make an active SIM card and later top it up using this link. Thank you!

Then you better go "opwaarderen" by an "opwaardeerbon". You can buy one in a Supermarket or Tankstation. 

I can't do that at the moment.  Is there an option to do this using a bank card?  Maybe there is a site where I can buy a voucher online?

I found the link https://gamecardsdirect.com/nl-en/kpn-10-euro/ Can I use it to pay for my number with this voucher if I'm not in the EU? Thank you!

Hi @Senator Frank, welcome! 

I am not familiar with the website you linked, so I can't advise you here. Maybe someone back in the Netherlands can get you a voucher and send you the code to top up your Prepaid so it's active again. Or maybe you can try to use another device to 

As mentioned above by @Noordzee it is important to keep your Prepaid number active. With active we mean using a paid option, like calling, texting or using data. When you don't make a paid action in 6 months, the number will be blocked for outgoing calls, texts and data usage. When you top up your Prepaid, the blockage will be removed till you reach another 6 months of inactivity. When you don't top up your Prepaid, the number will be disabled after 9 months. For more information you can check our FAQ (page is in Dutch).