Hi ​@ScottC 

If you have an Apple product then this information may help:-
https://support.apple.com/en-gb/108037?device-type=iphone

If you have ever synced your iDevice with iTunes you can go to the Devices tab in Preferences and hover over the backup of the device; the IMEI number will be displayed along with the serial number and telephone number.


If the phone is an Android and has been linked to a Google account then :-

For Android (Google Account):

1. Go to the Google Dashboard at dashboard.google.com on a computer or another device.
2. Sign in with the Google account that was used on the broken phone.
3. Scroll down to the "Android" section and click on the device name. The IMEI number should be listed along with other device details.
4. Alternatively, use the "Find My Device" feature (via a web browser or app) and tap the small "i" (information) icon next to your device's name.

If these tips are not helpful then you can contact the Live Chat as they should be able to help you ( as all networks use the IMEI of phones to verify that a device is valid and authorized to access their services) :-

https://www.idmobile.co.uk/live-chat

Type ‘talk to a person’ when you open the dialogue box to bypass the chatbot.
Please be patient as the agents handle a few conversations at any one time so there will be a delay in connecting with an available agent and also any replies to your query.
 

You can also contact iD Mobile via:-

Send a private message via their Socials (Facebook, X or Instagram)  
iD Mobile social media accounts:-

• Instagram: @idmobileuk
• Facebook: idmobileuk
• X (formerly Twitter): @iD_Mobile_UK

Hope this helps x