Welcome to our Community and thanks so much for your first post - sorry about any confusion caused with your new handset. If this was a replacement handset, you would just use your existing SIM.
Also, depending on the handset you have the the settings may not allow the SIM to know it's number.
I can see from your account that you have since been in touch to get this confirmed with us - I do hope that all is working as it should with your existing SIM in your new handset. Pop back if you need anything further