iMessage not displaying international dialling code instead of contact name

Hi,

I am having a problem with messages on my MacBook Pro and I was wondering if anyone can provide any advice?

Firstly if I try to send a new message to a contact from my Macbook it says message not delivered then I click on why and it says "<Phone number> (contacts) is not registered with iMessage"

If I send it from my iPhone it sends no problem and shows up on my MacBook Pro almost instantly but instead of displaying a contact name it will show a phone number with +44 prefixing it. However it will also display that contacts photo next to it... suggesting that it knows there is a link between the phone number and the contact. (On my phone everything is working as it should be and it still displays contact name)

If the phone number is saved using the +44 prefix (I am from the UK) then I don't seem to have a problem and it works as it is supposed to.

Couple of things I have tried already to fix it:

I have made sure I am using the same iCloud account for contacts on phone and Mac. As well as iMessage account.

My country code / language is set to the United Kingdom, I even tried changing it and changing it back.

I have logged out and back of iCloud and iMessage on both phone and computer.

This has only been a problem since I reinstalled the Sierra operating system the other day. Before that everything was working fine. Any suggestions would be greatly appreciated as I feel like I have tried most things now but I am sure there is an obvious answer glaring me in the face...

Many thanks in advance.