[Al-Khwarizmi]

That isn't typically allowed. Spanish people also can have several given names, but they count as first names, not last names/surnames. A bank would typically check your data against a passport or ID and wouldn't allow you to put the middle name in the place of a last name.

And if for some reason you managed to do it, you would be called Mr. MiddleName in all communications.

As a curiosity, Spanish people often have the opposite problem - for example, in academia, if we sign papers in the "natural" way (FirstName FirstSurname SecondSurname) we'll be indexed as Name F. SecondSurname, which is quite jarring for us because we typically go by the first surname, not the second. So many (probably most) of us hyphenate (FirstName FirstSurname-SecondSurname) to avoid automated systems (or humans from other countries) to extract our surnames wrong.