I paid for the vehicle, but they won't transfer the ownership.

Literally speaking,
I have paid the full purchase price for the vehicle.
However, they keep delaying the ownership transfer,
so I am posting this late at night
to seek advice from the members.
I made a big decision and bought a one-year-old used car
for 70 million KRW (not a brand new one).
I took out a 30 million KRW loan and brought the car home..
Even after depositing the full vehicle amount,
the existing capital loan has not been repaid,
and the ownership transfer is not being processed.
I was planning to buy through a dealership,
but since this seemed about 5 million KRW cheaper than the market price,
I chose a private transaction after debating between two options.
But the broker is making various excuses and won't complete the transfer..
The capital company that provided the loan is demanding
immediate full repayment because the transfer hasn't been completed.
What should I do in this situation? ㅠㅠ
(I am kicking myself with regret)
I am currently in possession of the car..
I tried to save 5 million KRW, but now I'm stuck in limbo..
What should I do?
I am shouting and pleading with the person who brokered the sale,
but can I take legal action?