Payless Car Rental They charged me $250 cleaning fee for excessive soilage.

I rented a car from Payless Car Rentals(Avis subsidiary) in Salt Lake City airport to use it during my outdoor trip across Utah's National parks.

When I returned it back a week later everything was OK, a member of their staff gave me a final receipt and said nothing. A couple of weeks later I was charged $250 fee for excessive soilage. 

I admit that car needed vacuuming due to some dust/soil that got in after my hikes. But that's it. No food stains, no smoking odor(I do not smoke at all), no animals hair whatsoever. Basically, simple car wash with interiour cleaning that costs about $14-18 everywhere would do the perfect job. That's what they have to do anywhere after each rental.

I tried to reach their customer service but they gave me a standart answer.

Please, advice what should I do.