Fuel missing after long-term parking - blatant theft, no feedback!

I parked my car with this organisation for 10 days. After returning, my petrol gauge showed that a nearly a quarter of my tank was missing. I brought this to the attention of the business and received no feedback! Besides the charges for parking, the loss of fuel amounted to around R300 (at current prices). This seems to be a new way of making money, as petrol in SA is a precious commodity. Not acceptable to me, as I entrust my vehicle to be handled professionally. I will certainly not support this business any longer. Pity!