Wrong Diagnosis on car

[SBP]

My Mazda 6 2.0 TDI Sport has been serviced since purchase by local main dealer. Had a problem of lack of initial power when pulling away then power and dark blue/grey smoke from exhaust.
This started just a few miles after it's 1st MOT, which as you know includes an emmission test.
Anyway, took into dealer, said they would run Diog test. Diagnosed turbo and intercooler problem. total cost £2525, which, as just out of warranty, Mazda would pay 70% as goodwill. My cost £757. Said smoke should cease after running car for approx. 250 miles.
It didn't, initial problem still persisted. Took back in, dealer said to run car for 500 to 1000 miles.
It still didn't cure the problem. Dealer carried out a diognostic test and found an old code on the EGR unit (Exhaust Gas Recycling), they re-coded and said I should not have any more problems.
I did, same as initial problem. Dealer then ran another diognostic test and diagnosed a faulty EGR valve, which needs replacing at £350. I asked why this did not show on initial diog test, they said "the turbo can mask an EGR problem". This sounded suspicious to me and I suspect they did not run aninitial test. Mazda would only offer 60% goodwill as car another month old. I argued and they agreed 70%.
Car has been better since, but I now get a whistling sound coming from the turbo.
I took the car to Turbo Technics for a specialist opinion and their 1st comment was "you have definately got a turbo problem (not had but got), it sounds like it is either out of balance or it could be damaged". Apparently this can happen if the turbo is not properly primed after fitment before start up. Turbo Technics also found the car to have a throttle problem, which could be electronic". They said they could not touch the problem as the turbo would be under warranty. They suggested I ask the dealer for permission for them to work on the problem.
I am now highly suspicious that the dealer did not run an initial diog test, replaced a turbo and intercooler that did not need replacing and have now replaced an EGR unit that has still not cured the initial problem.
Do I have a case to demand a repayment of my outlay Does this come under The Supply of Goods and Services Act and, as I paid by credit card, The Consumer Credit Act
Any guidance or comments would be very appreciated.
SBP

[old_andrew2007]

Bump

[Conniff]

Although you say it has been regularly serviced SBP, pull out your filter element and see if that makes a difference, a dirty one can give those symptoms.

[raydetinu]

Ask Mazda to send an engineer to look at car, seeing as they have paid most of the repair costs and still not runing right! they would then sort out with garage.