BKK take a week to produce a yearly statement, thst's why I moved to SCB. Take a photocopy ofevery page of your bank book and take the bank book. Remember to sign every page IN BLUE!
I'm on a retirement extension based on a non O-A obtained here in Thailand, not a visa from the UK. No insurance needed and as I am 78 I can't get Thai insurance, I've tried.
I had this problem last year so I moved the money to SCB who can print out a year and give a letter there and then. As a precaution, as I closed my BKK account, I got a statement from them- 4 months after my extension, then ,with the SCB bank letter from the start of that account- month 4 to month 12, CM Immigration were happy when I presented both, together with both bank books. Next year no problem as it is now firmly in SCB. Not sure what the policy of other banks is, but the week delay makes the statement invalid I think as Immigration want a one the same day or maybe not more than 1 day old, I think it depends on the office.
But it also says you must keep at least 400,00 all year, I have done that, but one bank account ends and a new one begins ( on the same day well before the 2 months minimum), it's the break between one account and the new one is what I am asking about.