If you write to Mazda with your VIN they can write you a letter for the DVLA to get it changed. They’re super friendly and helpful, I’ve just not sent it off yet as you need to send your v5 with it.
For me at the end of the day, the VIN is very clearly an import and not on the inclusion list for anything other than non-cat emissions, but testers seem to think I’m pulling their leg.