No refund of cancellation fee

I booked online and paid for a rental car on 17.01.2018 to be picked up at Schiphol airport on 19 April 2018. On 26.02.2018 I cancelled the booking telephonically and the agent assured me that the total amount would be refunded. No cancellation fee would apply due to the early cancellation. An amount was refunded 27.02.2018 minus a cancellation fee. In the terms and conditions it states that should Budget not suffer a loss due to cancellation no fee would be charged. They deny having such an agent who promised the refund and said they would trace the call I made and check. To date after several attempts to communicate with them I have had no success. I see there are many complaints about Budget - how do they run a business like this??