Power of a sub registrar, validity of a sale deed.

I gave power of attorney to a person and after some time I intimated him that I am going to cancel his power and cancelled his power. Both are registered. on the same day when I cancelled his power he intentionally made a sale of agreement with one person for 1,60,000 by getting 1,50,000 as advance and registration to be done with in three months of time.

The buyer did not contacted me until now. The agreement is made three and half years ago is it still valid. When inquired in sub
register office he asks to cancel the sale of agreement to sell it to other person. does the sub registrar has the power to reject on stating the sale agreement.