1998 Vauxhall Corsa cant use my car for more than 5 mins ?

Engine Mechanical problem
1998 Vauxhall Corsa 4 cyl Two Wheel Drive Manual 80.000 miles

hi im going crazy with a serius problem with my car .i have a corsa 1.6 16v sport r reg 1998 . my timing belt snaped on the moter way . so i had the head referbed £660 , he rang to say done pick up , wen i got near home about 16 miles away the car staled restarted but with a slight missfire , ever since its been getting alot worse . now thers blueish smoke from the exhoust alot . with mega loads of black sut in the tail pipe , also the plugs r getting full of black sut very quickly after about 2 go,s of 5 min run , the car only runs for bout 5 mins then stalles at lights will restart but i have to rev or it will stall again there is a very bad missfire after the 5 mins at lo throtle and the car sounds like a tank loss ov about 30% power too , ive changed map sensor thermostat sensor new plugs new ht leads its fine for the first 5 mins then prety much undriveable . i had a conpreshion test dun he said it wer fine but i wernt there wen he did it ? please please help ive only just bought the car had it 10 mins wen the belt snaped . and we have no money for a new 1 , thankyou , barry