Do you have your visa already? Pretty sure they will deny your application without proof of an exit ticket. That is what they did to me the first time I came here. I just bought a cheap throwaway ticket. Worked fine and I got my visa.
you’ll find that a lot in Thailand. They work with the banks. They will help you open the account and it will show the 800,000 you need. They don’t use your money. Just don’t over pay for the service.