Yes, write! Anything at all is better than nothing. Somebody will read it. If you ask your MP to get information from a government department/ask a question of a minister they are obliged to do so. So someone in that department will also read it and will be obliged to formulate a reply.
A couple of months ago we wrote to our Labour MP about Assange (we had to nudge her a couple of times!) and finally got a response from her (supportivish) and from a spokesperson for the prisons department (tosh). (I posted it here at the time). Every next expression of concern about JA will be registered and will add to the pressure on the government.
We are about to do it all over again with our new Tory MP. What the #### else can we do?