1) if power of attorney had been given by you to a person for sale of property and it is duly registered then the person has power to sell the property by entering into sale agreement
2) you have stated that power of attorney was revoked ? was intimation of revocation given in local newspapers?
3) you will have to challenge the sale agreement made by POA to third party if it was don e after cancellation of POA
4) please cross check whether sale agreement is duly registered now . if it is not properly stamped and registered then it is in admissible in evidence .
5) registration of sale deed can be done maximum within period of 8 months .
6) sale deed if registered can be cancelled by mutual consent of parties