Due to he increasing number of phone scams, all banks have been instructed to check whether every customer’s phone contract is under the same name as their bank account. When this is not the case, they need to see the customer in person to do an identity check.
The day for the next 90 day stamp is 90 days after the last stamp or 90 days after the last arrival in Thailand, whichever is later. It’s not connected to the visa or extension dates.
k just after letter is issued, but the bank cannot prevent you from doing it, they ask you to keep the money 4 months before issuing the letter (equivalent to 2 before + 2 after)
Being uncertain about your departure plans, and just giving the maximum days, whilst unsure about this number, certainly gave the impression that you are just trying to stay as long as possible. If you had shown a return ticket with a booking within 30 days I think you would not have had any problems. Impressions count.