Can employment be "terminated for cause' after you the employment contract expires and you resign?

My employment contract had a normal expiration fo 12/31/2009 and would continue unless terminated by either party within 45 days of expiration. Exactly 45 days prior I received notice that the contract would be terminated and a "new contract" would be in place after the first of the year. I expressed my dissatisfaction but continued to work diligently with hopes of resolving. When I finally got the agreement in February it was totally unacceptable. After trying to resolve for another month, I notified the employer that we were at a stand off and we would be canceling our relationship at that point. The employer still owed me substantial pay per the contract. Exactly 4 days after my notice to her and 2 months after the expiration/termination for convenience of my contract, she then sent notice of "termination for cause" in an effort to not have to pay the monies due to me. The questions are: Can someone get terminated for cause after they have already been terminated for convenience and informed employer that the relationship has ended? Basically terminated twice? Can someone get terminated for cause after they officially stopped working for the employer? Are there any consequences for the employer making false charges which are very transparent simply to avoid paying "severance?