NETS plugin doesn't send customer to terminal

-- HikaShop version -- : 2.6.0
-- Joomla version -- : 3.4.5
-- PHP version -- : 5.4.45
-- Browser(s) name and version -- : Chrome 48.0.2541.0 dev (64-bit)
-- Error-message(debug-mod must be tuned on) -- : No error messages from turning on debug mode and maximum error reporting.

The issue happens in all browsers.
The URL leads to the test product, which has to be bought to see the problem

Now, the issue we have is that the NETS payment method doesn't work as intended anymore.
For some reason it stopped working after the last september this year and we haven't made any updates or anything, until today, when even after the updates it didn't work.

Right now a customer can add a product to the cart, go to checkout, press "finish" and skip the entire payment terminal where they are supposed enter their credit card stuff, but instead of that step, the order gets "completed" as if they had paid. It's basically an instant redirect to the "thank you"-page with the order-info. No payment ever gets done.

There are no error messages or anything, NETS say they do receive a "register" request but that we never send the customer to the payment terminal.
They also say the NETS plugin doesn't redirect the customer to their terminal.

Is it just us or is the NETS payment plugin broken for some weird reason?
What can we do now to make it work again?

*edit* Seems it didn't create the topic in the right category for some reason. Can an admin move it to payment methods?

Yes, the problem seems to have been an issue with an old template-file.
Not sure how it wasn't noticed until now.

Thanks for the quick response!
I'll remember to check old template-files first next time.