Data Source not being dropped on publishing

Long story short:

A third party just did a massive code change for the front end as it is a developing platfrom and they decided to change the name of the server and the db.

So i simply went through all the relivant PBIXs and changed the server from the server name to the IP and also changed the DB from NM3-Live > NM-Production. It has worked for 99% of our models. However for one of them it worked in the desktop and it refreshes a treat, however on publishing it to the services, the old connection to NM3-Live is still there and so is the new NM-Production. 

This model is actually a child for a mini-project for sales and the mother model has worked fine. I have triple checked the connections in the desktop, there is nothing mentioning the NM3. Is there a way to find it using DAX Studio? Or has this PBIX corrupted some how? Any ideas?

I have tried:

- Using an old copy of the report also.

- I have deleted it from the workspace and app and tried republishing

- I have tried publishing it to a workspace which has never had this PBIX.