This issue is raised by others before, most banks like to see longer than 3 months window to stay in Thailand in order to open that account for you. Even though, non-O can be extended another 12 months to give you total 15 months the initial entry stamp is only 90 days (3 months) which is not long enough for most banks to agree to open an account for you. So bank is not refusing that stamp as non-O, bank is just telling you to return back after extending it for 12 months. Some went to Kasikorn bank and opened without any issue, so I suggest you try a few Kasikorn branches.
recently there are a lot of Bangkok bank related complaints on this forum, including mine, accounts and apps on freeze, 400k or 800k deposits on freeze for 4 months etc.
For the 1900 baht extension fees they always gave a receipt, at least on 2 or 3 occasions they kept the 100 baht change. I really can't remember if I received a receipt for residency certificates, first time I used for opening the Bangkok bank account and to get my car + motorcycle driver's licence, second time for the 5 year extension of those licences (so lucky they actually extended for 6 years). I did not mind those fees because I still saved a bunch because I did not use any agent or a driver school to get my stuff done.
I did not ask for an expedited service at the immigration, they wanted 800 THB. I thought it is the fee for this service. But I am used to not receiving back 100 THB at the immigration after handing them 2000 THB for an extension fee and before I paid 250 THB to get another certificate at another immigration. So this guy's tea money was something else
I had tons of uninvested cash in Fidelity and BofA brokerage, not accepted a few months ago. I know a few others who had same issue, possibly BOI recently changed the policy on this requirement.