Right, driving my s2 today, in second gear, put my foot down a bit, and bang from the exhaust, then loads of white/blue smoke, i thought shes blown up, so i got a tow to my lock up

i thought right wip the head off and see the damage, the car runs fine on idle, and when revved, oil pressure fine, no knocking, but the smoke was a white and blue colour, so i was thinking headgasket, so while taking the turbo pipes off i noticed the shaft wouldnt spin, and the little nut on the end was loose!!

so i just took the turbo off, and its seized solid, the turbo was rebuilt 3 months ago by universal turbos via pts in luton, 535 quid, my engine has done 4k since rebuild as in spec in sig, its a stage 2 turbo running 21 psi, they told me its fine for 21psi, so thats what i went for, ive heard a few people on here having problems with turbos latley not lasting long

i always do all the precations looking after the turbo and engine, so its not down to abuse,i use mobil 1 oil etc,

would the smoke indicate the turbo problem or have i done internal engine damage aswell?