Phone number that i don't have anymore registered to Apple ID

An old phone number that i don't have anymore is registered to my Apple ID. How can i remove it?

When i wanted to delete it the message says "This phone number is being used for iMessage & FaceTime. If you still have the iPhone that uses this number, turn off iMessage & FaceTime on it and try again"

but i don't have nither the phone number nor the iphone

how to do that ?