Warrenty that just wants your money

My gear box packed up and my van was taken to a friends very reliable mechanic in Waterfall till it could be seen to, I have an AMP Warranty so was not to worried as I only bought the car last year November and My services are up to date and on time as stipulated in my contract with AMP. The Mechanic stripped the gear box and put together a quote, on inspection it was found that a prop-shaft vibration had caused a nut to come loose which made the inside of my gear box like mince meat. Granted that I had just had a service in January my car was running very well and I had felt no vibrations of any sort up till this point. AMP refuse to pay my claim saying that I was negligent and that I should had felt the vibration and known it was my prop-shaft and gotten it seen to. Last time I checked I am not a mechanic and neither did I feel a vibration at any time in my car. The mechanic who serviced my car last also says that there was no vibration in my car when it was test drove in January and assures me that I would never have picked it up either way. The fact that the prop-shaft was vibrating means that it had failed therefore the damage caused by its failure should be covered. I have been made out to be negligent when I was not. It seems AMP are only interested in taking my money every month rather than covering my car when needed.