Hello @Yoong 

How much calling credit do you have left, could you call a number before purchasing the bundle?
Are you in the Netherlands and are you calling a Dutch number?
How long ago did you use any calling credit?

Calling credit remains valid indefinitely but only if you use some calling credit once every six months by calling, texting or using the internet.
If you do not do this, your number will be frozen after those six months.
From that moment on, you have about 90 days to save the number by topping up your calling credit.
During that time you can still receive calls or text messages, does that still work?
After those 90 days the telephone number will be permanently discontinued.

Warnings about this are sent by text message, but the phone must be turned on to receive them.

It seems like my credit is valid until the 8th of July, 2024, according to the kpn app.

I am in the Netherladns, but I was trying to call an institution in Germany and before buying this the bundle that I have bought did not work as well. I am quite urgent this time, so I have written this question.

My mobile data has been working fine until now, so I believe that my number has not stopped.

The text messages that I have been receiving until now were in Dutch, which I do not understand, so I do not know if I have received such warnings.

I do need to call people, so is there a way to use this bundle?

If the app says the credit is valid until 8th of July your number should still work, so that should not be the reason it's not working.

Trying to use any prepaid bundle for calling from the Netherlands to a number in Germany or any other EU country will not work anyway.
If you are in the Netherlands, prepaid bundles are only valid in the Netherlands.
You can call with it to any EU country but only if you are in any EU country but the Netherlands.

But calling from your normal calling credit to Germany should work if you have sufficient credit left.
Does calling a Dutch number work?