Shell V-Power - not much use.

On 3 April, I purchased R400 petrol at STEYNS GARAGE - Shell HERM**** WAY BOTRIVIER, Western Cape, 7185. The attendant refused the card, saying they are not really a Shell garage! How is one to know where the V-Power card is accepted, since they sell all the Shell products, wear Shell uniforms and the Garage has a Shell sign? I contacted Shell several times but nothing has come of it. IS the V-Power card worth it, since there seem to be pirate Shell garages?