what will be the best way to prove extreme hardship
First, if you were eligible to apply for adjustment of status with a waiver without leaving the country when you originally filed and have not left the United States in the interim, then you should be eligible to apply again without departing the United States. I am almost certain that you cannot reopen the case because it has been simply too long and the deadline passed. Therefore, the best route would be to apply again, but this appears to be a complicated case, and once a waiver has been denied once, the burden typically becomes even more difficult to meet when you apply again. Contacting an immigration attorney about this matter is advisable.