Here's what it looks like flat shaded, in cycles, with the settings. i only upped transmission to 1 and roughness down:
It looks like maybe your normals are flipped. Check this box.
If your glass looks like this -
Enter Edit Mode, select all with A, press Alt + N and select Recalculate Outside.
Your glass should look a bit better, but it looks to me like you should consider adding some supporting geometry on the top and bottom.