Booking and paying for transfer from airports ahead of a flight

When I couldn't get a lift from Dusseldorf Airport, I contacted the GetTransfer Agency and they send me a few quotations from close by taxi companies. I choose one and communicated directly with them. What followed where big delays of my 2 flights from Cape Town, and I had to correct my arrival times with the taxi company 3 times. In the end they had to decline because they had other commitments, which I fully understood. Unfortunately I had paid GetTransfer from South Africa already. When I contacted them and asked them to return the amount to me, they refused. I sent several emails explaining that there has been no damage to anybody as I had been able (and with difficulties for myself) to cancel the trip and to inform the taxi company in time. I think this comes close to *****. They might have kept an administration fee but not the full amount. In general I think with all the delays with flights it's not advisable to book ahead through agencies like this. I can definitely not recommend GetTransfer.