I've moved your post because the thread you posted it on is 7 years old. I have heard of someone getting this letter in the past, and it was literally a check to see if they were receiving the right amount of money for their needs. If you're worried you should try and ring, or ask someone to ring on your behalf to find out what they want to know.
BIS
Nothing on this board constitutes legal advice - always consult a professional about specific problems
