Why pay for swapping of cars?

The problem initially started when my fiancé got the courtesy car from the Europcar branch in Centurion. Everything went well. Got the courtesy car on the 21st of February 2022. He had the car till the 2nd of March 2022 when Europcar phoned us asking for the car back, because it is busy being sold. We made a plan, filled the courtesy car up and took it back the very next day, because my fiancé works far away. One of the consultants I spoke to also said when I asked her if we need to pay any additional fees or anything for the second courtesy car as a replacement as the agreement is suppose to be till the 8th of March 2022 for the first courtesy car, she told me no. There will be no additional fees as we are just swapping the cars. Then my fiancé had to wait after giving the car back approximately 15 minutes to be assisted with the second courtesy car. Last night we received the invoice that we have to pay for the swopping for the second courtesy car? How is this acceptable? We were asked to do this and went out of our way to get the first courtesy car back. And now we have to pay for the swap? Advise and assistance will be appreciated.