I was fired by my boss early this morning without notice, because I didn't have a company meeting yesterday (because I had a rest yesterday)

In this case, you can protect your rights and interests through legal channels. According to the Labor Contract Law, a labor contract must be signed within one month from the date of employment. Otherwise, you will start to be complacent in a month, and you will get double pay.

In addition to what I said upstairs, I would like to add that the situation in your unit is that you deliberately find an excuse to fire you. In addition to not signing a labor contract, it is against the provisions of the labor contract law. In the case of arbitration, you can ask for the basis of dismissing employees on the grounds of not going to work for one day. In practice, the enterprise rules and regulations of most enterprises are generally unfounded. Because this is based on 1, it should be legal; 2. Make it public, even if you just sent a message to your boss before the break. The practice of the unit is still illegal and needs to bear legal responsibility.

Let's talk about your evidence again: if you really can't find evidence, you can find two or three former colleagues to testify for you and explain your labor relationship with your unit. You can also apply for an arbitration unit; Your communication information can be used as reinforcing evidence. Finally, good luck.