Also, I cannot possibly rotate by hand the stator inside the rotor (completely stuck, whether the controller is connected to the stator or not).
If the stator is properly centred in the motor ring
(and both side covers are fitted correctly) you should be able to rotate the axle
(and stator assembly) using a 10mm open ended spanner without too much difficulty, but don't expect to be able to turn the axle just by twisting it with your finger and thumb.
If the covers are not seated properly, it may be possible for the stator to touch against the magnets, making it very stiff to turn.
Also, if any metal particles have stuck themselves to the magnets while the stator was removed, they could easily wedge themselves into the small gap between the stator and the magnets when the stator is refitted, even with the stator correctly centred inside the magnets.
If the axle is very tight to turn with a 10mm spanner, or makes a horrible grinding sound, it is likely to be caused by some form of physical resistance rather than the normal magnetic drag, and you will have to remove the stator and look carefully to locate the cause.
Unfortunately, if you are still experiencing the continual 5 flash fault code on the controller LED with the hall sensor plug fitted correctly, the controller could be damaged. And if the controller has failed, the motor is not likely to run, even if the axle does turn freely with the spanner.
Alan