4 months of deposits is not enough,and it has nothing to with Bangkok Bank. You need 12 months of deposits showing up in your bank book when applying for the extension.The 800k option is what you need to go for. The money has to be in your account at least 2 months prior to the day you apply for the extension.
I've been with Bangkok Bank and KBank for years. I've also used the same phone number for many years and that phone number is the number registered at both banks.I have never had any problems with anything connected to my phone number. BUT, according to KBank there are about 700,000 phone numbers activated sometime during 2022 (I don't remember the exact date) which are not registered to correct owners and does not match the number given to the bank. Many of those numbers doesn't even have a registered name. There are websites selling sim-cards which are pre-registered and that's not allowed.