Europcar One-Way Invoicing

I recently returned to South Africa for a visit in February, and rented a vehicle from Europcar. I used a 3rd party travel service (Trip.com) and paid for a package, opting to pay extra for one-way drop-off, as I would be landing and collecting the car in Bloemfontein, but returning it at OR Tambo. This was a significant premium on my total package, but I figured it was cheaper than a plane ticket to ORT.

Cut to the collection in Bloemfontein - I'm informed that the one-way drop-off will run me an additional R1900 (more than a flight), which will be charged to my deposit. I keep telling myself I already paid for this, but think that I must be mistaken. A couple of days later, I went back to the branch and requested to cancel the one-way drop-off, and return the car a day early to avoid the fee, opting to fly to ORT after all. The consultant said that because I had returned the car a day early, I would likely be credited.

We then reach a few weeks later, I get an invoice from Europcar for toll fees in the amount of R439. I do not dispute this amount, but what i do dispute, is the fact that according to my original invoice, I was charged, and paid for a one-way drop-off, which I did not make use of. Surely then, Europcar actually owes me the difference of R777 between my unused drop-off charge and the toll fee?

I've been sending emails regularly (I think I'm up to four now), but I still get emails saying the matter is urgent and I need to respond, they've been trying to call me, blah blah blah. Here's a thought - respond to my emails!

I'm not paying Europcar a cent because according to my reconciliation, they owe me money, not the other way round. Hopefully someone will actually respond to a freaking email now. Also, I'm not in the country, as I've tried to explain, so calling me will not work.