Do not despare - it is still alive.

Like any other gesneriad - it rots if overwatered. So it shoudln't stand in a water ever. If the roots are rotten - look at them and tweak - if they are gone - they will be falling off - you better restart it from part of a healthy stem you have. Method - sphag-n-bag. Barely moist sphagnum and get it covered.

Second option - they grow under lights and in relatively humid conditions. If your air is very dry - it can cause problems...

Third option - normally these plants are tough. What if the box got overheated in a mail or near your doors waiting to be picked up? It could cause a damage that would bring a gradual decline.

If I would grow this plant on a windowsill - I would use Oyama pot - and do not refill reservoir it until the soil is dry. It is kind of fleshy - so it won't die if dries a bit.

Regarding VB - since the purchase was done months ago - they are not going to replace it. Before you could call them during the working hours and ask for an advice. If it arrived cooked or frozen - the time to complain was at the same day or about. I do not think there is a magic word they can say - and it will recover - at that point.

Otherwise - this plant requires the same care as an AV, can take a bit more light. It is not as tough as Nematanthus "Tropicana", but it is not picky. VB soil is on a heavy side, I would repot it into something lighter- like AV soil split with perlite, at the same time look at the roots - if they are viable. Keep it covered for some time - but barey moist, not soggy.