Trish,(posted 8266 days ago)Pendle is quite right in all aspects of his reply.
I would also add that "going quiet" for a while, is probably also a tactic used by them, in order to worry you (some more). Imagine 3-4 Mths of no letters (you might be hoping in the back of your mind that they have given up the chase), and then another one comes through your letterbox.
This happened to us last summer, and we are at present waiting for their reply to our last letter, sent in early June.
When they do send you another letter, make sure you ask them to explain properly why it has taken them xx weeks/Months to reply.
Good luck
Stephen