You needed to have the network operator cancel that old number then send you a new SIM with the same number
Then it would work
Read this when you have time.
first look at this - If your iPhone, iPad or iPod touch is lost or stolen – Apple Support
Lost and Stolen phones are rarely ever seen again.
Risk Mitigation
Get your provider to
Cancel your SIM.
Send you a replacement SIM on same number.
You can then put the SIM in another phone to get the codes you will need.
Phishing warning
Unless you had a PIN set on the SIM the finder now knows your number so don’t respond to texts to sign into your account!
Resign to the fact your data is safe but you will never see the phone again