Hello @Kevin Lebon 

After making a T-Mobile account you need to add your subscription via abonnement koppelen. Have you done that?

Hi Yes I did, when I reach the point of giving the final code numbers, it says that an error occured and eventually never works.

Hi @Kevin Lebon, I have taken a look for you and I see that you have made an account with us in the past, for a previous order. This account was still linked to the cancelled order in our system, which prevented you to see the correct information about your current subscription. I have deleted the old account entirely, you can now register for a new account with the same e-mail address on our website. When you link the account now, it will automatically connect to the current subscription and you will be able to see all the correct information! 

If you have any other questions, please let me know. I am always happy to help!