3 interviews later.... HELP!!!

[ohhhtinalynn]

I am a US citizen. My husband is from Israel, and we have been married since January of 2010. In November of 2011 we filed our I-845 application and got a notice for an interview in Feb of 2012. We went to the interview, where we were only asked a few questions and then sent on our way. We didn't hear anything for months, then in August of 2012 they showed up to do a house inspection. All fine and dandy since we had been living together since 2009, but then all communication with immigration stopped. We waited almost 2 years and still had not heard anything from our lawyers nor from immigration, so we decided to get our local governor involved. After they contacted USCIS we were scheduled for a second interview in May of 2014. We went to the interview where they separated us and asked a bunch of different questions, mainly relating to events that happened almost 5 years ago, and mostly about our Israeli friends. This interview lasted almost two hours and still no outcome. We received ANOTHER interview notice for this past friday, July 2014. This interview was the same as before; they separated us and asked more questions, specifically about someone we had known at the beginning of our marriage and we are no longer friends with. This person had previously applied for a visa and was denied and deported, but we have not had contact with him in almost 4 years. She blatantly lied to us to try and get us to say something incriminating but it did not work. Then she started to ask about us having had anyone living in our home besides us. I had had a "friend" staying with us for a few weeks while she got on her feet, but we got into an argument over the fact that she accused my friend of raping her and then decided to move in with him two days after, obviously ending our friendship. It came to light during the interview that a "poison pen letter" had been sent to USCIS saying that I had been paid to enter the marriage. While this is false and was done with malicious intent, USCIS is now using it as their only reason for not approving or denying my husbands application. During the last interview she told my husband and lawyer that she would give us her decision, but then she called me back in to further discuss the person who wrote the letter and the reason we were no longer friends, as well as about the person who had been deported and our relationship with him. She then called in my husband, asked him the same questions, and escorted him out, no decision.

So, my questions are, can USCIS use this letter without any proof, and from a source that I and many other people consider not credible? How long is considered a "reasonable amount of time"? Is there any legal action I can take against this harassment? And is "guilty by association" a legal standpoint for them to deny the application?

Thanks