Thrifty Deposit refund denied due to flat spare tyre which I didn't use??

I rented a car from Thrifty because my car had been / still is in for repairs. Imagine my surprise when they turned up at my door and wanted their car back immediately. It seems that the consultant at the depot had not completed the renewal of the car rental. I was stranded in Moorreesburg and work in Cape Town! Now they are saying that I won't be getting my deposit back as the spare tyre is flat? I didn't even look at the spare tyre, let alone use it. The car wasn't inspected with me at the depot and I was just given the keys and told where to find the car. I spoke to a lady on the phone on the 10th of December and she told me that the deposit had been approved for refund to me on the 9th. No answer to email.