1) deed of cancellation of POA has to be executed by you and duly registered. in case the power of attorney is registered deed then you have to cancel it through a deed of cancellation/revocation & that too has to be registered.
2) you should intimate your father about revocation of power of attorney granted to him
3) also issue public notice about revocation of power of attorney
4) Rule 58 of registration act prohibits the registering officers from enquiring into validity of the document, Rule 26 read with Rule 58 reveals that it is always permissible for the registering officer to examine the document presented for registration as to whether the person who presented the document is entitled to present, whether such person is known to the officer or has been properly identified by the identifying witnesses, and also examine the document with reference to the various provisions referred to hereinabove. If any objection is raised, the registering officer has to consider whether the parties appearing before him are not the parties they profess to be, whether the document is forged and whether the document is presented without proper authority by representative, and whether the executing party is dead or not. In case, the registering officer is not satisfied, he can refuse registration
5) Under Section 71 of the Registration Act, the registering officer has to record his reasons for such refusal in book No. 2 and endorse the words "registration refused" on the document and when asked for, to furnish the reasons to the person executing or claiming the document. The reasons for refusal could be many and many more as seen from Chapter XXIV of the Rules. When the registration is refused, the person aggrieved has to prefer an appeal to the Registrar (Section 72) and if the appeal is also rejected, the remedy to an aggrieved person is to file a suit under Section 77 of the Registration Act for a decree directing the document to be registered by the registering officer.