R250 clamping fee from owner of Shell Select

It's that time of the year when parents are preparing for Back to School. I got to Protea Books and there was no parking. I see a Shell Select that I sometimes get fuel and goodies at. I thought I could park quickly and get the text book. I get back about 20 mins later and my wheel is clamped. I'm told by the owner that it's private property and I must pay R250 to unclamp my car. Is this legal? I paid the R250 that he claims goes to charity. What does the law say about the authority for clamping and fines?<br> There was another vehicle that was clamped at the same time. It was gone by the time I got out from speaking to the owner. Do some people pay clamping fees and others not?<br> There were open parking spaces. Customers were not turned away in the time I bought my child his school book. Does Mr Manie Coetzee consider the support he has previously enjoyed from me. <br> Does any business have the authority to fine customers for parking? He said there is no law or governance prescripts from legislation or Shell but it's his property and he can do this. <br> I was shocked at the ethics of this kind of arrangement.