Language School Certificate of Bank Balance for Self Sponsorship

I'm applying to a couple schools in Fukuoka Prefecture. I am self sponsoring and have more than the required amount saved to pay for a 2 year program plus living expenses. They require to show about $15k bank balance to cover the first year tuition and living expenses. Now they know I will not be working during my stay and I will not have an outside sponsor, so my first confusion is why are they not requesting the full 2 years proof of balance? And why are they requesting my work records like taxes and my business license (I have a w-2 job and my own business)?
The real question I have is they are requesting a "Certificate of Bank Account" Which none of my banks seem to offer exactly what they want. I can't seem to get a certificate issued with signature and stamp from my other banks. Does any one know what I need to request from these places to get what the school wants? Or is the school being suborn by not accepting a statement? Everywhere I see in reddit and other posts people say they sent a statement to their school, not a signed certificate. And I sent what one bank sent me which was an email verifying my balance based on a specific date, and the school edited it and told me to add the signature and seal. That feels quite fraudulent and I do not want to end up on the wrong side of immigration upon arrival due to following instructions like that as well as it makes me weary of the school.