It was a bad experience for my first investment.

At first I approached agent A to view the house (subsales, afterward only I found there are a lots people post the same ads under same company at Mudah), A said have to ask her boss B (her manager) to open the house for me as that's his customer.

After checking all I decided to paid deposit, but then B said there is someone pay earlier than me, so have to queue until his customer got loan rejected.
After a few weeks, A called that the loan rejected mean is my turn I can submit the loan. Then she comes collect the deposit and asked me to sign documents etc.
And now the banker C follow up my loan. She said she already check in system CRRIS, I need to settle my PTPTN loan then should be no problem atleast 70% I can get the loan. I settled then wait.

Few days later, A called me again said B want to cancel my booking, as suddenly his client got the loan approved. I don't care, I said is my turn you can't cancel like that.

After two weeks (within this period I keep calling and whatsapp C to update my loan status, but she always said busy will get back to me), C replied my loan got rejected, and she said already help to appeal but unsuccessful too. I'm thinking, isn't C need more supporting documents from me to appeal?

Can I complaint A with his company (or any related organization to sue him), or C (I'm thinking maybe can complaint to Bank Negara)

Can someone advice me?

Most probably... Best is post at property section...

Btw, the deposit taking process got documentation mentioning that that property will be reserved for you indefinitely?
Your loan is still not yet approved, thus I think they should be able to sell to others first.
Did they returns you the deposits?

usually purchasing form/booking form will state that SPA must be signed by buyer within 14days to 21days from the booking form date else consider as void contract.

from your case, i believe it is already exceeding 21days

i believe it is all about mutual agreement. as long as buyer's loan is approved, seller or agent won't border to abort the deal.
but refer to TS situation, his loan is not approved yet and exceed the time bar given, usually agent will just cancel his and refund the booking fee if there is another buyer which can fulfill the deal