Jet Airways — tele check in/ voucher upgrade

Ref: pnr earwzy, 9w 762, mum-del 15th march.

I called for a voucher upgrade and was confirmed that its done. I was allotted a business class seat (1f).
I received a call later, when i was intimated that my class of travel is not eligible for an upgrade. I wonder why jet didnt know it when they processed my request and allotted me a business class seat.
To make things worse, i was told that my initial seat (10c) is no longer available and cant be allotted to me. This seat was initially chosen and paid for, so its surprising that jet allocated it to someone else and made it unavailable to me due to their own faux passe.
Horrible service, and 3rd grade customer service!