probably a no-brainer, but...

[downandout]

I sublet a room in an apartment - no lease, no written agreement - for four months. All months were paid in full, cash, to the person I assume is the official tenant. When I moved out (after giving a reasonable amount of notice), I - mostly because I didn't want to send the keys back through the mail - didn't get the keys back to her right away. She sent me a telegram, threatening legal action. I did subsequently return her keys, but she is still sending me notices, invoices charging me for January, February and March(although I returned the keys at the end of January - after moving out December 27).

As far as I can see, she has no legal ground because we had no written agreement. Though I am quick to say I should have returned the keys more promptly, there was no signed contract and I don't see how she can prove that I did or did not return her keys. I can't find anything to disprove or support my belief, because I don't see anything that isn't specifically regarding an "official" tenant.

Just want to make sure that I can tell her to f#*! off without any possibility of legal ramifications.

[too trusting]

If I were you I wouldn't respond period. It sounds like you live in another state now. Just return any correspondence marked return to sender. She won't know where you are and she can't take you to court because she can't prove her case. If you respond then she has some sort of a paper trail. But again since there is nothing in writing, just blow her off, silently.