FFS Cop on. Agents exist in this universe to make the process easier for a fee. Illegal? Possibly but very grey. Who would police that ? Immigration? They are the ones accepting the applications.
Sure that’s normal that the agent has your passport for the week or two that it takes to process the visa/extension, but an agent holding your passport over a barrel until you cough up enough funds to cover the amount is not an “agent”, just an extortionist.
Not trying to be sarcastic in the least but you need a new agent.
WTF would an agent hold your passport until you have enough funds. An agent does what they need to do without you needing funds (which is why many people use agents).
You can’t get the initial Non O, nor the first year extension using monthly transfers. If your embassy doesn’t provide an income affidavit then the only option is banked 800k. After the first year extension then you can switch to 12x 65k monthly transfers.