I changed my phone number and I want to unlink former number from my Apple ID and it doesnt allow me saying iMessage and Face Time are connected to it. But it is not, it is disconnected. There is online possibility to deregister your number but there is no my country in the country list and I cannot enter country code manually
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.
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.
I cannot Deregister iMessage online because there is no my country in country list and I cannot enter country code manually
