If ING is able to suggest Twitter/WhatsApp as communications mediums instead of email, then it means they are either incompetents, or it means that they are doing it on purpose, due to Twitter/WhatsApp conversations being superficial and the services very volatile. Maybe they don't want you to store your conversations forever in an easily searchable archive. Maybe they don't want you writing long and clear messages describing your problem.

Either way, it's time to switch banks. And it's a good thing that you told me about it, as in Romania we also have ING and was considering then for my business account.