Are you in Bangkok? I experienced it before. Other banks in the city will just give you the bank statements they normally give. Sad to say the immig is looking for another type of bank statement.
The banks at Chaeng Wattana, below the immig office knows exactly what the immig is looking for. It will just take them 10-20 mins to process, so you can go there instead.
There are 2 things where I see the confusion here.
1. Language barrier - "if you asked them while talking fast or using unusual words like "con period" , or maybe you have a strong accent, or they were not paying attention with your question and only understood some words from what you said. There is a big possibility that there was a miscomminication and they didn't underatand your questions clearly and they just blurted out an answer.
2. I think you worry too much - the con period is there, and the bank documents are there, even photo copies of your updated bank book are all submitted. Then you also mentioned that you have been doing this for years. My suggestion for you is to not worry so much - you did the right thing.
-you kept your money untouched during the 21 days con period. They call it prrof of financial capacity for a reason.
-they gave you the visa extension because you conpleted the requirments.
-job well don for you and the officer.
(Now if you want to confirm that something was wrong with it. Maybe you can try withdrawing your money during the con period on your next extension) please update in this group what happened, so we will be enlightened.
Also, is this you first time having a 1 year working visa? If that is the case, they will give you a month Visa (under observation) before they give you the full 1 year.
You can leave the country but be sure to return before that 1 month visa expires.
In some cases, the immigration from your ciuntry will be yhe one who will ask for you work permit. (Again, in some cases) this is to prove that you are really working here in Thailand.
My suggestiom is, go straight to the labor dept. Once you get your Visa. The process will just take 1-2 (business) days.