Can you be terminated for violation of company policy, if you wernt aware of policy?

I was let go for posting my opinion about a current coworker off the clock on my time on a multi media website. There wasn't any personal information posted just what I thought about her. She was apart of the leadership. The next day I was called in and let go for violation of companies social media policy. I explained that I wasn't aware of the company policy about social media, nor was I giving any employee hand book regarding company policies. At this time I was shown a copy of the policy. I Mentioned that I was not on company time it was my personal time after work. Is this grounds for a wrong termination suit?