This is my first post so please bear with me - i also know very little of cars!!

My 3 year old C4 picasso ran out of warranty at the end of last month. It developed a problem on 10th March (21 days within warranty) and returned it to the citreon dealer i bought it from, they diagnosed the problem as a blown turbo.

They fitted a new turbo but told me there was a problem with the enigine and in their opinion it needed replaced! They were to contact Citreon Warranty to get authorisation for this.

This is where the problems start - my last service was carried out by a local independant garage and the car needed an oil change and oil filter. The receipt and invoice was in the log book. 3 weeks later i get a phone call back from the dealer saying that warranty will not authorise the repair as the oil used in the service was not the correct grade as noted in the maintenance book. I called citreon customer service and they got back to me basically saying warranty were within their rights to do this and sorry but there's nothing more they could do - warranty was invalidated!!

I went along to the dealer today, got hold of the service book and had a word with the mechanic who worked on the car. He says the problem has been that the pipes which distribute the oi to the engine and turbo had become "gunged up" starving both the engine and turbo of oil, resulting in the turbo blowing and the engine knackering. He also told me that citreon had issued an "info rapid" to the dealers identifying this problem as it had obviously happened to other cars!!

On closer inspection of the maintenance book it states that for diesel engines 10w40, 5w40 and a.n.other type of oil should be used - the servicing garage and my invoice clearly states that 10w40 magnatec was used for the oil change (which was almost 12 months ago!!) I called Citreon Customer service again and asked how the warranty could be invalidated when the garage had used the grade of oil stipulated in the maintenance book - they're looking into it!

Is this a case of the warranty dept trying to wriggle out of paying for what will be an expensive repair or am i royally fooked!?!?

What steps should i try next if warranty still refuse to authorise the repair?