Additional charges even though no damage and full tank

I rented a car from Budget on 5 Oct 2017, returning on 9 Oct 2017 at Cape Town International Airport. I prepaid the reservation (Reservation number 1 ********** -ZA-6) of R1931.50. For the 5 days 1000km was given and my entire trip took less than 800km. The car (a Hyundai i20) was given to me extremely dirty (the car attendant even mentioned it).

Upon returning the car, I filled up at the BP at the airport (filled the car up full) and drove the 700m to the rental bay. I however have an additional charge of R158, heaven knows what it's for. Emails to Budget go unanswered. Their after sales service seems to be non-existent.

I returned the car full with no damage and well below my allowed mileage so why am I being charged extra? I have rented cars from other companies and never had this poor service. You have lost a customer.