jaguar XE R Sport 65

i have had a warning light come on stating contaminated Adblue and the care will not restart in 500 plus miles, booked into local garage who could not find the fault bit a knott sensor was showing up on the  system as a warning 

booked into Jaguar and on route the warning disappeared Jaguar checked it over, charged me £90 as they charge £180 an hour and found nothing as no faults were showing

 I then decided to replace the sensor

Two weeks later the same issue, booked in again got down to 40 miles before the vehicle would not start drove towards garage and at almost the same spot the warning disappeared again 

This time Jaguar said if they could not find the fault no charge

So after checking they have informed me that they think the local garage overfilled the Adblue which does not make sense in that the warning went off and came back on 2 weeks later

Has anyone else had this issue or maybe knows what the issue is?

Thanks for reading