"changed professionally" you say? :-? :-? :-?
Any bike mechanic with more than a couple of brain cells should know that you don't need to touch chain adjustment when removing the rear wheel, the chain tension should have been exactly as it was before you took it there - sounds like the individual who performed this "service" (and I use the word advisedly) for you didn't have a clue what they were doing - take it back to the place and demand that they sort it out immediately. If they argue the toss you could threaten legal action as they've returned your bike to you in an unsafe condition >>
