Nissan NV200 clutch judder

Hi , hope someone has some advice ...... my NV200 van is just 3 yrs old with 14k on the clock , for a long long time there has been funny noises from the engine which the dealer cannot trace despite it going in umpteen times . The main one is a judder when you pull away in 1st gear . It doesn’t do it in any other gear , if I’m fully loaded with a trailer , it isn’t any worse . From 2nd gear onwards it pulls like a train . On it’s last service , last week , I went out with a technician to try to replicate the noise but couldn’t . The noise is more prevalent on a hill start & with full lock on . Later in the day they called me to say that my clutch pedal is high which indicates a failed clutch and therefore the noise . ( 3 weeks ago In was in for diagnostics on the noise for 2 days and they couldn’t find anything amiss) . They say to fix the noise will be £1200 as it isn’t a warranty item as I must be driving with either my foot on the clutch pedal, too much weight in my van or an overloaded trailer. I can honestly say that it is neither of those things , I drive 2 other cars with no instances of a failed clutch and have never had a clutch in any car I’ve owned in 35 years of driving .
I’ve contacted Nissan uk who say that the clutch needs to be disassembled (at my cost) in order to look at it , then go from there . Which I don’t feel is very fair .
I’m no mechanic but if your clutch fails then your revs increase and your not moving anywhere , not just a momentary juddering in 1st then every other gearchange is perfect , on the motorway it will cruise happily at 80 and want to go on.
It doesn’t seem like the clutch has gone ?