breaks

hi there! i need help ( advise) about my 2008 Nissan Quest SE. i am having
problem with the breaks.i had the change and put new wheel bearings hubs
and break shoes on both rear wheel.,after job was done,i  took the car for
driving test.the first thing i  have noticed the yello ligth( VDC OFF) came
on,and then while i was driving my car made unexpected ,sadden  stop. very
dangeros situation that could cost bad acciedent. so took the car back to the
shop,and have them do  the inspaction,but they could not find anything
wrong,but since that day my car now makes this sadden ,unexpected very
dangeros stops,like ur breaks get locked in while u are driving.u dont know
when it happens,because it cuold happen at any time.i have stop driving my
car,because i am scare,it;s very dangeros situation.,i had to take  my car to  
the shop and have mechanic do the computer diagnostic, and they could not
find any issues..but i still have this problem,and i wish, that some one could
give me the answer,or any clue what could cost this problem! thank you