No service after transfer from prepaid to subscription

Hello!

I have just changed my KPN prepaid card to a yearly 5G contract onto a new SIM card (iPhone XS).
The clerk told me it should be working after 5 mins but it’s been several hours now and still no service. (I have already turned on /off my phone and automatic for network is on)

Can you kindly suggest what I can do online before I head back into the store again?
Thank you!