For procuring community certificate you have to apply for the same in writing to the Revenue department or Tehsildar within your residential jurisdiction.
After applying for it you should comly with the legal requirements namely, the copies of proof of residence, your father's community, your residential proof, your educational certificates etc.
If the authority is rejecting the same with any reasonyou may try to rectify and re-submit the same.
If that is not possbile then you may file a suit to declare your commnunity by the court based on the documentary proof you possess and a direction toconcerned authority to issue you with the relevant community certificate based on the court judgment.
Take the help of a lawyer when all your efforts with the revenue department fails to yield any fruit,.