Oil Seal Change then Turbo Blows!!

Hi To Everyone.

I have an early 1999 TD5 Defender 110.
I have on going problems with this Landy that all came to a head today. I have had a major oil leak which turned out to be the front crank shaft seal. I picked it up from the Land rover dealership and 24 hours and 30 kms later the turbo seems to have blown (heavy clicking/whiring noise, loss of turbo power and then plumes of white smoke coming from the exhaust).
What was not right, was that the oil pressure warning light on the dash didn't go out (after I picked it up from the dealership) I noticed this at the dealership and they took the dip stick out to show there was oil in the engine. They fobbed me off by saying that the engine just needed to warm up, and the light would go out. It didn't!
I checked the oil level again, and it was ok.
I am wondering why suddenly has the Turbo gone. This has to be more than a coincidence.
Please help, as I am about to go into battle with the dealership.
Thanks.

Dont want to scare you bloke but .....
Oil in the engine does not mean the oil pump is working. Oil pressure should come up just by cranking the engine on the starter let alone running it and waiting for it to warm up.

The turbo bearing has blown because you had no oil pressure. It relies upon full oil pressure to float the turbo shaft. No oil pressure = fried turbo bearing in very short time plus untold other damage to your engine internals.

Go back and insist they sort it out or take them to trading standards.