When I had this problem with the Bangkok Bank statement showing both FTT and TPP, I requested a statement through the banking app, printed it, highlighted all the transactions, went to the branch and asked them to confirm that all the transactions were from abroad.
An hour or so later, I was given letters confirming each transaction was a FTT. I submitted those with the printed out 12 month bank statement, and a printout of my bank book. Chaeng Wattana accepted that and since I leave the 800k untouched, building up a small surplus with the interest, have had no problems since.