Transmission Issue

If this happened after a service in the shop, I'd bring the bike back to them and tell them about the problem.
Is your shifter hard to move? Or does it move like it is supposed to but the bike won't change gear?

same thing happened to me recently on my sons yz 125. I tore it down and the problem was minor. One of the clutch plate ears had fractured and migrated over into the shifter mechinism sticking it into gear. Drain the tranmission oil and remove the left engine side cover. check for any fragments and compare it with the manual. I then had to install a new clutch basket and plates as it appears the slight grooves in the basket was the original problem that started the whole mess. A couple gaskets a new clutch and a basket fixed it without splitting the cases or any tranmission problems. Has been fine since!

Worth a try.

Ok Exactly what "service" was done at the shop?

if they worked on the clutch or trans then its most likely "their bad"
if they put tires on or a topend its "on you"

Once we determine this its easier to work with them. If you have an idea its most likely in their realm then very nicely talk to the service manager and explain the likelyhood that the problem is theirs sine they worked inside the clutch cover recently. Explain that 2 weeks waiting for their mess up is unacceptable. You were there first when they messed it up so you should have a better spot in line than the guys that just brought their stuff in. Worst case you an file a small claims suit for $25 (Not sure for canada though.)

now if they worked no where near your clutch or trans then buck up and accept that mechanical things do break.

My kids bike was stuck in gear after several thousand in mod work was done. turned out one of the screws that held the shifter drum acutator in place came out and jammed. yes it was the mod shops fault but easier to fix myself than sending the motor back.