Ad blue use age

[curlywurly1971]

Hi , I have a B9 model and topped my ad blue tank up at 65800 miles , so going on the range of I think I read was 12500 miles for a full tank, It should of given me a top up warning around 77000, yet I had nothing, so I decided to top it up anyways and only managed to add around 3lts into the tank until it overflowed!,  so does anyone have any ideas as to what is up?.

Many thanks,  Gary