If a person insults the agent of Beis Din, it is permitted to repeat the insulting words to the Beis Din, and it would not be regarded as Lashon ha'Ra.
If a person fails to heed the instructions of Beis Din, he is liable to be excommunicated. (1)
A person that is non-compliant with a decision of Beis Din regarding a financial issue is warned three times, on Monday Thursday and Monday again, and if he continues to be recalcitrant, then he is excommunicated. (2)
Excommunication may be immediately revoked by the Beis Din. However, if the basis of the excommunication was because he insulted Torah sages, the excommunication period may not be less than thirty days.
There is a dispute between Abaye and Ameimar whether an excommunication may be revoked ONLY by the same Beis Din that implemented it.
In Bavel excommunication is only for seven days; the same as a Nezifah (censure) in Eretz Yisrael. A Nezifah in Bavel is only for one day.
A righteous person has the power to revoke a decree of Hashem Yisbarach.
A BIT MORE
1. Beis Din may also Machrim (place a curse on) a person that does not heed them for a period of sixty days, and they may publicize his wrongdoing. They may also take away his property and make it Hefker (ownerless).
2. A person is only given a warning prior to excommunication involving a financial matter. However, if the person insulted Torah sages, he is immediately excommunicated.