Concealed Cistern Flush Pipe Nightmare?

Some 4 months ago I purchased a Roma Vanity Suite comprising a basin and back to wall toilet fromTaps4less to fit into a newly built ensuite . It all looks fantastic and very plush But.....
The builder's original plumber had grumbled that the flush pipe supplied was incorrect and he had to make up one from elbows , connectors and sealant . The toilet would only flush towards the back of the pan rendering it unhygienic and useless . A second plumber was called and he said immediately stated that the cistern outlet was too low to allow the flush pipe to fit and he would be unable to fit it.
The cistern has already been mounted as high in the housing unit as is possible so there is no adjustment available .
I have spoken to the suppliers on numerous occasions via telephone and unanswered emails and have been informed that they sell loads of these units every week , nobody else has problems and that I am fitting it wrong .
The flush pipe has to be cut so close to the bend that the more it is inserted into the cistern outlet then the angle of the " horizontal " part of the pipe is foced lower and at an angle some 5 inches below the pan inlet .
I am informed by Taps4less that the pipe has to enter the pan inlet at an angle in order to fit but surely this will distort the flush cone and create leaks .
In any case mine is so far away even this could not be an option .
I am now in a situation that means that the plumber says the goods supplied will not work , and the suppliers say that there is nothing wrong with goods .
I am running out of options and unless someone out there can offer some worthy technical advice , I can only foresee a lenghty and unpleasant trip via Trading Standards to reach an outcome .
All I want is a loo that works !