Contactless problem

This contactless thing in the fnb card is a problem. At first it did not ask for a pin at R50 or less. The other day I accidentally tapped my card at the petrol station for over R300 and the transaction went through without having to enter a pin. On questioning this i was told if I don't want to use it i can stil swipe or use the chip and no restrictions can be done on this. My worry is what happens if i don't realize my card is gone someone can use my card to Tap and Go with my money. What can be done about this problem