Hi Natimweembe
welcome to the Apple (user-to-user) Community.
Re: problems with my iMessage and face time : activation is always unsuccessful : What do I do?
Thank you for posting your question to the Community, and for including your iPhone model, and up-to=date iOS.
You need a strong wi-fi (and / or cellular data) signal, and especially for FaceTime.
You may want to:
Check that you have a contact card for yourself, with email and phone number listed in your contacts app.
Check that you are signed in (to your iPhone) with your correct Apple ID:
How to: Sign in with your Apple ID - Apple Support
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In order to activate Messages app : How to: Set up Messages
How to: Add or remove your phone number in Messages or FaceTime - Apple Support
In order to activate FaceTime app : How to: Set up FaceTime on iPhone - Apple Support
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If apps are still not activated 24 hours after set-up:
Trouble-shooting activation: If you can’t turn on or sign in to iMessage or FaceTime - Apple Support
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If you still need more info. / help / support / contact (online chat, phone. email etc.):
Messages Support webpage: Messages for iPhone, iPad, Apple Watch, and Mac - Official Apple Support
or
FaceTime Support webpage: FaceTime - Official Apple Support
All the best :-)