Also, to confirm...are you using soil? Calycina prefers a nice airy mix. I use 1/4 inch Orchiata bark, #3 perlite, and 1/4 inch LECA (expanded clay) balls, all equal ratios. In a pinch, a high quality fine grade orchid mix (no soil) from your local garden center will do.

Soak ingredients overnight and rinse well. Rinse off as much of the old potting soil as you can from the root ball.

While you are able to see the root ball and root stem, check for signs of rot (stringy, squishy, stinky, discolored/mottled roots, squishy, stinky, black or brown root stem). If all looks okay, pot up in the new mix.

You may need to water more frequently, until the orchid mix has had time to "saturate" and hold water more readily. The overnight soaking prior to using helps a bit, but the mix still may dry out rather quickly until it adjusts.

Thank you so much! I will do as you suggest and update in a bit. Will the yellow leaf recover or should I remove it?

It wonxt recover, but you can leave it to fall off on it's own. It is an old leaf, anyway :)

So I've been feeding it when I water but today another leaf turned yellow and fell off :( I don't know what to do

Haven't had a chance to get some orchid mix yet but it's still in the pot it came in so wouldn't they have sold it in the appropriate medium?

Not necessarily. Many nurseries root cuttings in cheap/incorrect medium because it's cost effective. If you received it from an ebay seller, they may have potted it in a medium that works for their environment, or may have also used a cheap medium for cost effectiveness.

Does that pot have drainage holes? If not, you need to use a pot that does. Most hoyas cannot stand wet feet and will decline rapidly. You really need to check the root system for signs of rot or poor health.

Ok so I just re potted into orchid mix and checked the roots. They seemed fine? And yes the pot has drainage holes.

As you can see, another leaf is turning yellow. If this one dies there's only be 4 leaves left. I'm losing hope :(

That lower stem should not be turning brown:

I'd cut back to green tissue, and re-root.

Ok, thank you for all your help. How should I do that? Do I need it cut for a few days before I put it back in the pot?

Cut where green tissue begins and immediately pot up. No need to wait for cutting to scar :)