Union Bank Of India — Bank has deducted amount for bank mistake

Sign verification of NACH form bank has deducted amount for rejection and approved. Where sign verification forms were rejected giving reason of sign differ. Where my sign is same and same forms were approved by same bank for same sign when I reapplied. Then why bank has charged me for rejection. It is completely bank mistake then why should I have been charged. I want my amt back which is deducted under reason of rejection .i tried to contact bank Branch and they said they can't help. Which is totally wrong.