If you are fit and mobile you realy should try to get your extension yourself. It's not just the money you will save but also the multitude of issues that could cause you problems later on. For example if you get a new passport your local office will not transfer your stamp. You will have to go to the office that issued your stamp. It realy is not duffucult and if you present yourself well at immigration the officers should be very helpful. It would help you to get what is required from your bank if you get an IO to write out in Thai what they want to see.
I am not sure what your problem is. Bank statements for 12 months showing a transfer from abroad of
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baht or more is what is required. You might also need to show statements from the bank the transfers originated from. I'm not sure who is refusing to give your what.
I have just changed to monthly payments. I was not asked for anything from my Thai bank. I printed off statements from the banking app and highlighted the transfers. I also had to provide my uk bank statements to prove where the money had come from. My Thai bank book was up dated on the day and also showed all 13 transfers. I had my Wise transfer notes at the ready too but they were not required. I got the extension with very little hassle. Bangkok Bank.
TM30 should be filed within 24 hours of taking up residence in a private house or hotel etc. The property owner is responsible for doing it and it has no expiry date. Some immigration Offices require a new tm30 to be filed with them on returning from an in country trip while some don't. It can be done on line.
The 90 day report tm47 has an expiry date exactly 90 days from the date you entered Thailand or received a visa extension. If you leave the country within the 90 days it re sets when you come back. It can also be done on line but will be rejected if your tm30 is not up to date.
I hope that explains it. For the finer details ask at your local immigration office.