Millennium BCP - Not supported new currency

Hello! I am writing this complaint because there's no other way to communicate to bank's advanced technical assistance. I've been trying to make some payments to belarusian internet shops and my payment was failing. I called support to resolve this situation and they told me problem is with 3DSecure, unlocked it and I tried paying again - it failed with a new error (ISO code not valid). I called bank again, they checked and asked to try to process payment for the third time - it failed with same code. I had suspicion that problem is with new (denominated) currency introduced in Belarus, BYN instead of old BYR. Since Millennium couldn't help to clarify it, I called Belarusian company Assist that is responsible for these payments and asked them for help. They confirmed that though payment fails at 3DSecure step, the problem is with new currency, Millennium doesn't have it in place (they checked their logs). It was introduced in 2016 so I would expect it to work by now. Assist's support told me that bank can communicate and their technical specialists are ready to collaborate.
So I called Millennium support again to ask who I can contact on this matter, ask if BYN is planned to work with Millennium cards, but they couldn't help me and told there's nothing I can do. I am not complaining exactly about currency missing, but mostly about not having an active point of contact where I can ask such questions or make my suggestion to the bank.