Which Contract Controls?

I was a highly valued employee for a large media company for 12 years. During that time, it had three different owners. For ten of those years, I had a contract that clearly stated that if I were terminated without cause, I would recieve 6 months severance. Two years ago when my contract was up for renewal,
the new company stalled my new contract.
I was told that everything was fine, and that the lawyers were just slow in getting the papers to us. I went to the VP of the company numerous times to inquire about the contract. More stalling, and more verbal assurances. Finally, after almost a year, I was presented with a completely different contract that stated that in the event of termination without cause, I would be entitled to only 3 months severance, or the amount of time left on the contract, at their discretion. I red-lined it and sent it back to their lawyers. They responded by stalling again for another 7 months. After I wrote an e mail to my supervisor, I was presented with yet a different contract that again contained the 3-month severance clause. I once again did not sign it. While we were still in negotiation, there was a mass layoff, and I was terminated without cause. My questions:
Since they were continuing to pay me under the terms of the old contract while we were negotiating the new one, are the terms of the original contract (regarding severance) still in force?
I recieved a severance agreement letter upon termination, to which I responded within the 19-day time limit imposed by them, but I did not sign it. They are now not responding in any way to my inquiries. I have recieved no money at all since the day I was let go. What are my legal rights?