This is too real to believe. I believe one can restrict contacts from sending pm to them via their account settings if they really want to do so. I clicked the link to your handle and  I must say what I saw there was laughable. So you mean you can ban an account from sending one DM without the owner of the account doing so and this makes me wondering if you are a staff with the social media platform you mentioned there or you want the owner of the account to give you access to their handles so you could do such which I believe is not possible and can never happen so in that case, it would be nice you come up explaining yourself properly so that members here could get your point straight.