Do you know that you've definitely overfilled your Adblu tank only we had this last year while at Isle de Rey where it dropped from 4,000 miles to the countdown of doom.
I put in 7 litres of Adblu so the bastid obviously didn't have anywhere near 4,000 miles of Adblu before we started the trip.
Anyway we reversed our holiday because the countdown wouldn't clear... until 80kms later, then we're back at 5,500 miles but on our way back to the UK.
If you've definitely overfilled it then try and siphon off some and drive around in circles if you have to while sloshing the Adblu around and hopefully diluting any urea crystals building on the sensor or the tank itself... that was our case, I feel for you mate.