Hi @John836 and welcome to our forum! I'd be happy to help you with your prepaid questions and I'll answer them in order:

1. Is the prepaid-SIM practivated?

It is not

2. If not, can the activation be done in foreign countries (using roaming or online)?

It cannot be activated outside of The Netherlands, so the best advise I can give you for this is to activate it when you’re here. 

3. How long will credit be valid?

It has no expiry date, however, make sure to use the connection once every six months. If you don't the connection will be blocked, and if it's then left untouched for another 3 months (9 months of no usage in total) it will be terminated. 

4. Will the validity be extended on usage (phone call, SMS) or only on recharge?

On usage, an SMS is the safest way to register usage. So make sure to send a text message once every six months. 

5. How long are Opwaarderen-cards valid?

Good question. I believe that depends on the card specifically and when it was bought. You can check the validity date of the card on the card itself or on the receipt you get once you’ve purchased one. 

6. Can Opwaarderen-cards be used in foreign countries (using roaming or online)?     

It's not possible to use these abroad. You'll need to call 1244 in order to activate the card, and that's not possible abroad. You can, however, add prepaid credit online. This does work when you’re abroad. 

Regarding the chat bot, I'm sorry to hear this wasn't helping you properly. The only reason I can think of is that it wanted a postal code with letters, along with the numbers. So, say, 1033AA for example. Luckily you found your way to the forum though, so should you have any questions in the future don't hesitate to make a topic here!