  The non-association of coronal mass ejections with high energetic flares is
sparse. For this reason, the magnetic conditions required for the confinedness
of major flares is a topic of active research. Using multi-instrument
observations, we investigated the evolution and effects of confinedness in an
X3.1 flare, which occurred in active region (AR) 12192. The decrease of net
fluxes in the brightening regions, near the footpoints of the multi-sigmoidal
AR in photosphere and chromosphere, indicative of flux cancellation favouring
tether-cutting reconnection (TCR), is observed using the magnetic field
observations of HMI/SDO and SOT/Hinode, respectively. The analysis of
spectropolarimetric data obtained by the Interferometric Bidimensional
Spectrometer over the brightening regions suggests untwisting of field lines,
which further supports TCR. Filaments near polarity inversion line region,
resulted from TCR of low lying sheared loops, undergo merging and form an
elongated filament. The temperature and density differences between footpoints
of the merged filament, revealed by DEM analysis, caused streaming and
counter-streaming of plasma flow along the filament and unloads at its
footpoints with an average velocity of $\approx$ 40 km s$^{-1}$. This results
in decrease of mass of the filament (density decreased by $>50\%$), leading to
its rise and expansion outwards. However, due to strong strapping flux, the
filament separates itself instead of erupting. Further, the evolution of
non-potential parameters describes the characteristics of confinedness of the
flare. Our study suggests that the sigmoid-filament system exhibits upward
catastrophe due to mass unloading, but gets suppressed by strong confinement of
external poloidal field.
