they have messed up your tuning. similiar jack *** mechanic tried it on my car , only thing is i smelled a rat in the first 30 minutes of his inspection and told him to back off.
my old mechanic was not available at that moment hover he showed up after 3 hours , fixed up the messed timing of the point and drove her back to his workshop. he put in an hour , did complete tuning with tappit setting and mixture repositioning.
MASHALLAH , my car is running smooth again with no more black smoke.
now the difference is that my car is a petrol charade where as yours is a deisel hilux so better to get more suggestions from others. Also visit the 3 s dealers atleast 5 of the good ones you know to get an idea.
after that try finding an honest mechanic.
as for the blasted fools who tried ripping you off the 15000 bucks. The same amount will haunt them and go out of their pockets two folds.
give lots of sadka and zakat . Also alot of Tauba.