Tempest Car Hire *****s client money

Hired a car from Tempest in December, paid for 3 days and then extended my rental for an additional 2 days.

Returned the car a day earlier with approximately 700 kms travelled within the 4 days, with a daily allowable distance of 200 kms/day. Received my invoice which reflected the wrong day returned and over 1300 kms recorded.

I am owed money and have since spoken to and emailed representatives regarding this to which i have had no response - Is this how Tempest conducts their business, by *****ing peoples money?