Could be a number of things causing this. Need a bit more information.
Did the mechanic verify that the wheel cylinders are working?
Did they change the brake hardware like they are supposed to?
Did they install the shoes in correctly (there is a leading and trailing shoe)?
Did they verify that ABS system is functional?
Did they flush out the brake fluid?
Which drums did they use?
Which pads did they use?
You mentioned "drums" - I'm assuming that you meant the friction material and not the drum itself. If it was the drum itself, why did they replace it so many times, was it warped?
My suspicion is the shoes are on backwards and/or the original brake hardware was reused. Drum brakes are self-energizing, meaning that once the leading shoe makes contact with the drum, it will pull the trailing shoe into position and you can brake. Springs will pull the shoes back away from the friction surface once you release the brake pedal. If the shoes are installed backwards, the shoe will make contact with the drum face and not let go, even when you release the brake pedal. One of the tell tale sign of a shoe that is turned around is a banging noise when you first hit the brakes.
Could be something else as well - parking brake cable set incorrectly. Brakes adjusted too tight. Etc.
