There actually is no affidavit for opening a bank account
@Ma***
. :/
Many banks want a proof of address from either the immgiration office or from your consulate before they will let you open an account.
Seeing as you can't get a proof of address form from the immigration office in Bangkok unless you're on an extension AND have done at least one 90 day report, the only way to get the proof of residence certificate is from your consulate.