Disk brake brakes work poorly after annual maintainance
If the pads have oil on them they need replacing. The discs can be cleaned if done properly and carefully. If the LBS did the work, take the bike back and they should put it right. 

From the sound of it, I would also be looking for another LBS. If they cannot service brakes and keep the oil off they are at probably sloppy - but even the best shops have the odd incident. However, as they returned the bike to you in that condition, it is dangerous, they have let poor work out the door. My future custom with them would be in serious jeopardy.....