Notarized document rescinding a contract to sell is not required

Dear PAO,

I agreed to sell my land to Badong when he offered to buy it for a certain price. He made a partial payment, and the remaining balance shall be paid in two equal installments. After that, we will execute a contract of sale. We signed a contract covering the transaction, and it was also stated therein that non-payment of any installments would result in the automatic cancellation of our agreement. Unfortunately, Badong went bankrupt, so he failed to pay me. I told him that the contract was already canceled and I was going to sell the same property to Gina. Badong got furious and claimed that there was no valid rescission of our contract. He further said that rescission must be made in a duly notarized document. Is this correct?