machine rejected my coins and now they want me to pay

These guys are just thieves. I tried to pay for the road but it rejected about ten of my coins leaving me thinking that the machine is just broken. So I went, thinking that nobody's going to blame me since the machine didn't work and you could clearly see that on the video. I was completely wrong - they sent me a charge for $60. I wrote back an extremely friendly letter explaining all the situation and offering to check the video and I also attached a $3 check to it. Their reply was that they can make discount and offered me to pay $10. Hey, it's your machine that didn't work, why should I pay??