Using the high-resolution observations from the New Vacuum Solar Telescope (NVST) jointly with the Solar Dynamics Observatory data, we investigate two successive confined eruptions (Erup1 and Erup2) of a small filament in a decaying active region on 2017 November 10. During the process of Erup1, the overlying magnetic arcade is observed to inflate with the rising filament at the beginning and then stop during the explosion. In the hot EUV channel, a coronal sigmoidal structure appears during the first eruption and fades away after the second one. The untwisting rotation and disintegration of the filament in Erup2 are clearly revealed by the NVST Ha intensity data, hinting at a pre-existing twisted configuration for the filament. By tracking two rotating features in the filament, the average rotational angular velocity of the unwinding filament is found to be similar to 10 degrees.5 min(-1). A total twist of similar to 1.3 pi is estimated to be stored in the filament before the eruption, which is far below the criteria for kink instability. Several hours prior to the event, some photospheric flux activities, including the flux convergence and cancellation, are detected around the northern end of the filament, where some small-scale EUV brightenings are also captured. Moreover, strongly sheared transverse fields are found in the canceling magnetic features from the vector magnetograms. Our observational results support the flux cancellation model, in which the interaction between the converging and sheared opposite-polarity fluxes destabilizes the filament and triggers the ensuing ejection.