That's the first time it's been mentioned here - must be pretty recent. The phone number is genuine (Kidlington Oxford Audi) but it's odd they haven't provided a reference or any further details. I guess it's just a boilerplate recall letter as they can't be arsed to produce a different one for each callback.
Give them a call to find out and let us know please?
It would worth a while if you can please mention your model year and engine power.
So other people can also understand correctly.
There are quite many petrol engine variants 1.5 , 2.0 then TFSI 35 , TFSI 45 and so on.
Mine is TFSI 45 2.0 petrol MY20 have not received anything like that yet.