I am a first time Calamondin owner. I can't seem to keep the plant happy.

I live in London so I keep it indoors.

I bought it in July and it was somewhat matured with oranges alreadg. First had it in a direct Southern exposed window. It was dropping leaves and this forum had another users post that suggested the light was too strong. Based on the advice given there I moved it across the room (about 20 feet) so the light wouldn't be too direct but still bright. I also watered jt less frequently based on another post that seemed to work. I had been doing a few times a week and another post said to only water once a week or 10-14 days when it looked thirsty. The plant stopped dropping leaves. It didn't grow any new leaves or oranges but held on to the ones it had.

Near October early November as the light decreases jn the UK I noticed the oranges started to shrivel at first. Then leaves brown and and dropping. The whole back side is the plant is dead.

I moved it to. Small table closer to the southern window about 4 feet Away. I also have watered it about once every 10 days by giving enough until it comes out the bottom. The dying part seems to have stabilised and the green part reached towards the light but its not looking good.

There's also a spot of weird whitish area in the dirt and sort of the base of the root. Is it fungus? Pest work?

What am I doing wrong? Should I add some fertilizer? More water? Less water? Light?

Im Basically a completely inept plant parent who can only keep succulents Alive! I thought the calamondin would add decorative warmth and interest to make my apartment homey. Now it is making it look like death among us! Ha!