You violated the school's paper completion time, which led to the delay of the paper. A thesis cannot be awarded a degree or diploma without passing the defense.

No , you 're going the wrong way. At present, the school is not withholding your diploma and degree certificate, but that you have not met the conditions for graduation and degree certificate. If you pass the defense, the school will naturally give you an award. If the defense is passed, the school will still detain it, which is illegal. You can report the situation to the education administrative department first. You can't file a lawsuit directly.