In answer to your question, it is not unheard of on the forum, although 6 months is a long time.
Did you send your review form by recorded delivery, if you did check on line if and when it was delivered.
If you did not then contact PIP helpline:0800 121 4433 and ask if they have received your review form which you sent over 6 months ago. Even if you sent the form by recorded delivery I would still contact PIP to see what is happening with your review form.
Gary
Nothing on this board constitutes legal advice - always consult a professional about specific problems
