Wheelynice
All you can do is explain what you do and why.
There are two key requirements for therapy, first it needs to have been prescribed by a Health Care Professional, as you don't have the original letter could you speak to your GP, they may have a copy of the original letter on your medical records or they might be able to write a new one.
Secondly, the therapy must be required to stop your health deteriorating, again your GP may be able to confirm that is the case.
Gordon
Nothing on this board constitutes legal advice - always consult a professional about specific problems 
