[HELP] Xperia T Doesn't boot into Fastboot

[suicxde]

So I flashed a firmware way back and now I wanted to install a recovery inorder to install a custom rom. But my device\ doesn't go to fastboot mode.
I tried installing TWRP via APP and it says its flashed but its not booting into recovery.
is there any method to flash a custom recovery?
PS- Tried using ADB Shell too