PLEASE HELP! What is happening to my Calathea Zebrina? - More Info below

As many threads I’ve read, I started my plant mama journey with a Calathea Zebrina (Unbeknownst to me, how tricky these gorgeous plants are)

It was bought in the summer, after a few weeks of moving my beloved Freddie around, learning his watering & light needs I found his happy place & he was thriving. I use only rain water, mist every day & he was doing great.

As winter came along I noticed the leaves browning and others turning yellow. I snipped some yellow ones off & trimmed the browning - this seemed to help. However as we’ve come into winter & the use of heaters I noticed him struggling, unfortunately my partner knocked him over - though he seemed okay. A week or so later I noticed one, then two of the leaf stems sprawling out and dropping down the side of the pot & he was no longer doing his prayer motions up & down the plants are known for. I decided to repot & wash the roots wondering if it was root rot as I had given a good watering after the knock-over & when poking down and around the soil with a chopstick It felt as though the soil was clogged & airflow was nil. After repotting (& realising I shouldn’t have done so in winter; I live in Australia) He spruced up for a few days, however day by day he’s declining and the stems are all dropping, one by one. The leaves are still green & lush looking, however the stems feel quite moist and some almost soggy.

Please help! Have I doomed my beloved Freddie to an early death? Is there anything I can do to revive him? Or is he in shock, and will hopefully bounce back & up in time?