Hello, Madhelen.
Thank you for visiting Apple Support Communities.
I see you have tried some troubleshooting steps on your own with the issue persisting. There are just a couple more steps that I could suggest from the attached section below. Make sure that the devices or contacts that you are sending iMessages are iOS devices and have iMessage enabled on their device.
- Make sure that the contact trying to message you isn't blocked in Settings > Messages > Blocked.
- Make sure that the contact you're trying to send a message to is registered with iMessage.
- If the issue occurs with a specific contact or contacts, back up or forward important messages and delete your current messaging threads with the contact. Create a new message to the contact and try again.
- If the issue occurs with a specific contact or contacts, delete and recreate the contact in the Contacts app. Create a new message to the newly created contact and try again.
- Back up and restore your device as new.
iOS: Troubleshooting Messages
http://support.apple.com/kb/ts2755
Cheers,
Jason H.