iMessage isn't working on my Macbook pro

Yesterday, the iMessage app on my MacBook(15-inch, early 2011) stopped being able to send iMessages. Everything I tried to send would be sent as an SMS, and the app stopped receiving any messages at all even though I was texting and receiving texts from my phone. The iMessage app on my computers says that every one of my contacts "is not registered with iMessage" - not true, since I can still send regular iMessage through my phone or my iPad. On the Message setting on my phone, the Text Message Forwarding option only shows my iPad, when before it showed both my iPad and my Macbook. I have no idea what changed to cause this.

I have tried every piece of advice I could find online, including:

-Uninstalling and Reinstalling Yosemite on my computer

-Restoring a backup of my phone

-Restoring a backup of my computer

-Turning off and turning on Cloud for all my devices

-Repairing the disk on my computer

-Unauthorizing and Reauthorizing my computer to my Apple ID

-Making a new apple ID and linking that to my Phone and and Macbook to try and make iMessage work through that

I'm waiting for a call from Apple to see what to do about this. Can anyone help?