Showing error message to customer when the order price is under certain amount

-- HikaShop version -- : 2.6.4 Businness
-- Joomla version -- : 3.5.1
-- PHP version -- : 5.6.1
-- Browser(s) name and version -- : Chrome

Hi. I'm using bank transfer as my payment method and I've set a mininum price to 10000 in its restrictions. My problem is that when the user's order amount is under 10000 just a "Thank you" message is shown to him. I want to show him a message that his order is not valid.
I have checked the "banktransfer_end.php" file and tried to write an if_else statement to check the $this->amount and show proper message, but that isn't working.
Could you please tell me that where I should put my error message or what file i have to edit?

Thanks.

I'm using Bank Transfer method. After clicking on Finish in the checkout I show the customer a some message to assure him it was successful. My problem is that after clicking the FINISH i the checkhout, if the order price is above 10000 everything is OK and the message( that i've set) is shown to him and I can see the order create in the ORDERS section in hikashop. But if the price is below 10000 nothing is shown and just a THANK YOU message is is displayed!
A picture of my checkout is attached.