Bang thud that you feel, or bang thud that you just hear?
If you feel it, I'd strongly suspect the shocks. They don't need to be leaking to have failed, and the "bounce test" they do for an MOT tells you nothing.
If you are simply hearing it, then I'd suspect the front anti roll bar bushes - subframe out job to do these.
Also - have you used decent parts, because some garages fit utter rubbish that literally breaks as soon as weight is put on the wheels.
How often does it make the noise, and what are you doing to provoke it? Smooth/rough surfaces, cornering, speed etc...