Probably got a dud. I've seen wheel bearings on these cars crap out anywhere from 50,000ish miles to some of the ones on the highest mileage cars haven't even been replaced yet.
I thought you were always worried about having a shop install parts you supplied because of warranty problems down the road.
It's now down the road, do you have any warranty with those drums/wheel bearings the shop supplied and installed?
Edit: I found on the MItsu canada site you get 12 month 20,000km coverage on over the counter parts.
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View my fuel log 2014 Mirage SE wussie cvt edition. 1.2 automatic: 37.7 mpg (US) ... 16.0 km/L ... 6.2 L/100 km ... 45.3 mpg (Imp)