If, as I understand, you have given a power of attorney to someone and you wish to cancel it, I would do it through a Notary Public be means of a deed of revocation of a power of attorney. You avoid having a power which the beneficiary may use in the belief that you had not given proper instructions for it to be cancelled. The other possibility is for the beneficiary to sign a letter undertaking to not use the power of attorney under any circumstance. This serves as a formal notification, as he states he is aware of the prohibition.
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