Dang, its looking sad. Is that white stuff on the soil surface mould? If it is, I'd guess overwatering.

I'd still change the soil to very porous one, mine is in fine-ish orchid bark and couple handfulls of perlite; it holds VERY little moisture. And still I water it just once a week, week and a half.

Rubber plants have big thick roots that store water for a while. If you use regular potting soil, add 50% perlite to it.

It's only just come from the nursery a few months ago, and I've watered it once since then! Crazy! Would succulent potting mix have a similar effect? It also holds very little moisture