From what it sounds like, I have to say this, though you have done a ton of work, it sounds like you have missed a step.
Here’s what I would suggest: start from the beginning (I know this will take some work) and then work through each section of the transmission to ensure that it is hooked in correctly. All it takes is something relatively small, like a clip inserted backwards and the transmission acts just like you have said it is acting.
I honestly suspect that as you go through things that you will find that you have turned a spring or springclips around so that while they look like they are installed correctly, they are really backwards so that the clutch plate and pressure plate, for example, are not exerting pressure and completing the mechanical linkage you need to make things work.
Indeed, I think you will find that you may have even inserted the clutch plate or pressure plate incorrectly so that instead of pushing forward when you release the clutch, they are come apart. I realize that mechanics have told you everything looks okay, but, since your Mondeo isn’t moving, then something’s obviously wrong.
In your checking, I would pay special attention to the clutch springs and the pressure plate springs to ensure they are working correctly. Likewise, I would check the throwout bearing closely. Though it can honestly be inserted in one direction, you may find that you have inserted it incorrectly so that the device that is key to proper clutch operation — the throwout bearing — is inserted so that it is working incorrectly. Or, if the device is inserted correctly, it is possible that the springs that are suppose to help it engage correctly and disengage correctly have either been swapped or they are turned around.
I hope this helps. Let me know what happens.