Selective treatment at Porsche Johannesburg

I saw a car advertised that I wanted and sent an email followed by a visit to Porsche Centre in Johannesburg. I got finance pre-approved from Wesbank on top of the cash sum that I wanted to put in. I was told the car is at the workshop and would be out in a few days. A week later I was shown the car and told my offer was valid. That was on a Friday where they took my trade-in car for evaluation. On Monday, I received a call and was told someone else came in that Monday and made an offer and hence the car was no longer available. That smacked like unfairness in my view. What happened to first come first served? I tried calling and left messages for the sales manager. No return calls. I'll take my R1m+ elsewhere.