I feel for you. I spilt a latte under the driver's seat a few months ago. For days we were blaming the children for doing something unspeakable in the car, and then the truth dawned when the cup rolled out from under the seat
We tried cleaning it ourselves but nothing would get rid of the terrible smell. In the end we had it professionally valetted, which included steam cleaning the carpets etc, and using some sort of enzyme cleaner which apparently eats up the bacteria from the milk. It smelt a bit weird for a few days, and then we realized that the smell had completely disappeared.