Payment of all installments without interest

Dear PAO,

I entered into a contract to sell concerning a parcel of land from a certain developer in Bulacan. We agreed that the subject property will be paid in installments for 120 months or 10 years at a stipulated interest rate. During the fifth year of our contract, I realized that I had enough money and would already like to settle my outstanding obligations. When I informed the developer about my intention to pay in full, it insisted that I still needed to pay the interest as stipulated in our contract, whether I paid in advance or not. Can I already pay the price in full, and would paying in advance negate the payment of the stipulated interest?