Enterprise Saying I Owe Them £14000 For Putting Different Fuel In Tank.

Hello everyone. I'm seeking advice on this situation. I rented a van to move in Europe, I'm from US, and put the wrong fuel in it. HOWEVER I was instructed to more or less. During the walk around of the car, I have a video, the worker was telling me about the fuel. He said it was half full now, already some BS, and I have to return it the same way but then he said you need adblue (had NO idea what it was) and bring the receipt back. I asked him "what is adblue?!" "He said it's another type of fuel". So my thought was they got some new eco friendly fuel out here. I then asked "Can I get it at any gas station" and he said "yes!". He NEVER distinguished between regular diesel and adblue and NEVER showed me the two separate tanks or anything. So when I went to the gas station I put adblue in it and that was the end of that.

Is there anything I can do since I was INSTRUCTED to use adblue and wasn't shown the two separate tanks or told anything about using regular diesel? I've never used a diesel car before as I'm from the US.