"we could possibly complete the deal by Power of Attorney"
I don't know but I find it hard to imagine a legal instrument like that being possible to set up wholly remotely without some sort of face to face interaction.
I suppose it might be possible by post but even at the best of times that would probably take at least a couple of weeks.
One possible solution might be to ask your abogado if they could fax or email you a headed letter, ideally notorised, stating the situation then try your luck at the border with it.
Horrible place to be and hope it works out for you.