I am an expat living in the Netherlands and thus have multiple sim cards. Recently I changed from a prepaid sim to a KPN contract. 

Today when I removed my KPN sim card and switched to my international sim and then changed back to my KPN sim card I got a pop up screen saying that my Sim is locked and that I need to provide a numerical password. I have only had this sim for two days and have not set up a password. 

How am I supposed to unlock my sim card? I cannot even call the KPN contact number as the sim card is locked. This is the worst customer experience I have ever had with a telecommunication company.