Car dirt film

[Jessicabirkin]

I thought my car was just dirty so wasn’t too worried. But I have had it jet washed and cleaned today and struggling now. The rear of it seems to look not at all shiny and to touch feels like it has a film of greasy dirt this is also on the rear windscreen. Thought it might have been from a de-icer that I used but not to sure now. What can I use to get it back clean and what possibly caused this?

[Jessicabirkin]