I do not have my iPhone anymore, new service with new company. how can I deregister my iPhone

Log in to your Apple ID that has your old phone information and remove that device from it.

Here is some good information on what to do Remove a device from Find My iPhone on iCloud.com - Apple Support

Axel F.

Follow this link—>Deregister and Turn Off iMessage - Apple Support

It looks like we had different interpretations of the question. So now either interpretation is covered 😏

Looks like we are in a good place then.

Axel F.