3D Chamfer should work, but it doesn't. In fact, the tool leaves an awful lot to be desired. I re-created your object by
...Drawing a profile consisting of a Spline (2 straight sides and curved bottom) and a Line;
...Copying them and moving the copy 0.75mm in the Z direction;
...While the copy was still selected, resizing by 20mm in X and Y;
...Extruding the original composite profile downward 2.3mm;
...Lofting between the original composite profile and the resized copy;
...3D-Adding the loft and the extrusion to make a flat "chamfered" entity 3.05mm thick;
...Applying Bend Sheet to create the curvature.