:welcome:Superfuel to the forum, I am relatively new here myself.
As to the problems you are having.
I haven't used evo-stic adhesive before, but is it possible that it was out of date this could be the reason it hasn't set? I never use PVA I always use an acrylic primer, However you did follow the manufacturers reccomendation.
Also you say you removed MDF which was on the floor and exposed plasterboard! The plasterboard is probably there for fire reasons and or sound proofing, Im sure someone else will be able to give the exact answer. Did you put anything down on the floor or did you just
tile on top of the plasterboard?
What I would have done is put a good quality
tile backer board down on the floor on top of the plasterboard, such as hardi backer board, and then i would have tiled on top of that with a good brand of flexible
tile adhesive like a Bal make. I never used the ready tubbed stuff for floors, I always use the bagged stuff you mix your self.
I hope this may help you but i am sure yoou will get loads of more questions and answers shortly.