Deregister iMessage in Ivory Coast, côte d'ivoire

You can de-register using an Android device.

Where is the SIM with the Old Number, If it is not with you or you have given it back to the Carrier Service Provider, Then don't bother about it? You don't need to de-register it.

If you have it with you and want to use it with an Android device then put the SIM on any Phone (Apple or Android) and follow the GIF

Insert the same SIM into an Android or an iPhone. You may deregister iMessage online

Watch the GIF below. Here I have used another iPhone for the demo but for you, it may your choice. Android or iPhone device.

If you already tried (to no avail) all the steps provided in this support article:--> https://selfsolve.apple.com/deregister-imessage/, please contact Apple Support directly and explain your problem. Use this link:--> Get Support

Regards

Giulio