When you go to the ESA face-to-face - make sure that you have a copy of any correspondence that says you have difficulty talking. Yes, they should have a copy - but don't let them pretend they don't know. Do not force yourself to speak. If you need to only communicate with pen and paper - do so. Hopefully, the assessor will realise they have wasted your time and send you away! But don't put yourself under extra stress trying to do more than you would normally do. It's up to them to manage the situation - not you!
BIS
Nothing on this board constitutes legal advice - always consult a professional about specific problems